WO2013173513A1

WO2013173513A1 - Wide angle imaging directional backlights

Info

Publication number: WO2013173513A1
Application number: PCT/US2013/041235
Authority: WO
Inventors: Michael G. Robinson; Graham J. WOODGATE; Jonathan Harrold; Miller H. Schuck
Original assignee: Reald Inc.
Priority date: 2012-05-18
Filing date: 2013-05-15
Publication date: 2013-11-21
Also published as: EP2850472A1; JP2015526923A; IN2014DN09298A; US20170235040A1; US10175418B2; US20130307831A1; EP2850472B1; KR20150021937A; CN104303085A; US9678267B2; KR102269725B1; JP6305987B2; EP2850472A4

Abstract

An imaging directional backlight apparatus including a waveguide, a light source array, for providing large area directed illumination from localized light sources. The waveguide may include a stepped structure, in which the steps may further include extraction, features optically hidden to guided light, propagating in a first forward direction. Returning light propagating in a second backward direction may be refracted, diffracted, or reflected by the features to provide discrete illumination beams exiting from the top surface of the waveguide. Viewing windows are formed through imaging individual light sources and hence defines the relative positions of system elements and ray paths. The uncorrected system creates non-illuminated void portions when viewed off-axis preventing uniform wide angle 2D illumination modes. The system may be corrected to remove this non uniformity at wide angles through the introduction of additional sources away from the system's object plane, additional imaging surfaces, and/or by altering ray paths.

Description

Wide angle imaging directional backlights

TECHNICAL FIELD

[01] This disclosure generally relates to illumination of light modulation devices, and more specifically relates to light guides for providing large area illumination from localized light sources for use in 2D, 3D, aad or autosiereoscopie display devices.

BACKGROUND

[02] Spatially multiplexed autosiereoscopic displays typically align a parallax component such as a lenticular screen or parallax barrier with an. array of images arranged as at least, first and second sets of pixels on a spatial light modulator, for example an LCD. The parallax component directs light from each of the sets of pixels into different respective directions to provide first and second viewing windows in front of the display. An observer with an eye placed in the first viewing window can see a first image with light .from the first set of pixels; and with an eye placed in. ihe second viewing windo can see second image, with light from the second set of pixels.

[03] Such displays have reduced spatial resolution compared, to the native resolution of the spatial light modulator and further, the structure of the viewing windows is determined by the pixel aperture shape and parallax component imaging function. Gaps between the pixels, for example for electrodes, typically produce non-uniform viewing windows. Undesirably such displays exhibit image flicker as a observer moves laterally with respect to the display and so limit the viewing freedom of the display. Such flicker can be reduced by defocusing the optica! elements; however such defocusing results in increased levels of image cross talk and increases ^•visual strain for an observer. Such flicker can be reduced by adjusting the shape of the pixel aperture, however such changes can reduce display brightness and. can comprise addressing electronics in the spatial light modulator. BRIEF SUMMARY

[04] According to the present disclosure, a directional illumination apparatus may include an imaging directional backlight for directing light, an illuminator array for providing light to the imaging directional backlight and an additional optical element that alters the optical system of the imaging directional backlight to provide a substantially uniform 2D illumination mode. The imaging directional backlight may include a waveguide for guiding light. The waveguide may include a first light guiding surface and. a second light guiding surface, opposite the first light siuidittii surface.

[05] Display backlights in general employ waveguides and edge emitting sources. Certain imaging directional backlights have the additional capability of directing the illumination through a display panel into viewing windows. An imaging system may be formed between multiple sources and the respective window images. One example of an imaging directional backlight is an optical valve that may employ a folded optical system and hence may also be an example of a folded imaging directional backlight. Light may propagate substantially without loss in one direction through the optical valve while counter -propagating light may be extracted b reflection off tilted facets as described in US Pat App. Sen No. 13/300,293, which is herein incorporated by reference, in its entirety,

[06] Directional backlights provide illumination through waveguide with directions within the waveguide imaged to viewing windows. Diverging light from light sources at the input end and propagating within the waveguide is provided with reduced divergence, and typically eolliniated, by a curved reflecting mirror at a reflecting end of the waveguide and is imaged towards a viewing window by means of carved, light, extraction features or a lens such as a FresneS lens, For the on-axis viewing window, the collimated light is substantially parallel to the edges of a rectangular shaped waveguide and so light is output across the entire area of the waveguide towards the viewing window. For off-axis positions, the direction of the collimated li ht is not parallel to the edges of a rectangular waveguide but is inclined at a non-zero angle. Thus a non-illuminated (or void) outer portion, (that may be triangular in shape) is formed between one edge of the collimated beam and the respective edge of the wa veguide. No light is directed to the respective viewing window from within the outer portion and the displa will appear dark in this region, it would be desirable to reduce the appearance of the dark outer portions for off-axis viewing positions so that more of the area of the waveguide can be used to illuminate a spatial light modulator, advantageously reducing system size and cost.

[07] In general with this and related imaging directional backlight systems, not all the backlight area may be useable dne to vignetting at ^'high angles. Modification of the system may overcome this limitation by introducing light into regions that are void. Such .modified illumination apparatus embodiments may lead to increased brightness, local independent illumination and directional capabilities,

[08] According to a first aspect of die present invention, there is provided, a directional backlight apparatus comprising: a waveguide extending between an input end fo receiving input light and a retleciive end for reflecting the input light back through the waveguide; an array of light sources disposed at different input positions in a. lateral direction across the input end of the waveguide, the waveguide having first and second, opposed guide surfaces^' extending between the input end and the reflective end for guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from the reflective end into respective optical windows in output directions distributed in the lateral direction in dependence on the input positions; and a control system arranged to selectively operate the light sources to direct light into a selectable viewing windows, wherein, the reflective end converges the reflected light such that, .reflected light from light sources that are offset from the optical axis of the waveguide fails to illuminate outer portions of the waveguide, the waveguide further comprises sides, extending between the input end and the retleciive end and between the guiding surfaces, that are planar surfaces arranged to reflect light from the light sources, and the control system being arranged, on selective operation of a first light source to direct light into a viewing window, to simultaneously operate a second light source that directs light reflected by the reflective end and then by a side of the waveguide into the outer portion of the waveguide that fails to be illuminated by the first light source.

[09] According to a second aspect of the present invention, there is provided, a directional backlight comprismg: a waveguide extending between an input end tor receiving input light and a reflective end for reflecting the input light back through the waveguide; and an array of light sources disposed at different inpu positions in a lateral direction across the input end of the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding light forwards and back along the waveguide,, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from the reflective end into respective optical windows in. output directions distributed in the lateral direction in dependence on the input positions, wherein the reflective end converges the reflected liaht such thai reflected liaht from light sources thai are offset from the optical axis of the waveguide fails to illuminate outer portions of the waveguide, and the waveguide further compose sides* extending between the input end and the reflective end and between the guiding surfaces, that are arranged to reflect the light incident from a light- source into the outer portion of the waveguide that fails to be illuminated by that light source.

[ 10] According to a third aspect of the present invention, there is provided, a directional backlight device comprising; a waveguide extending between an input end for receiving input light and a reflective end for reflecting the input light back through the waveguide; and an array of light sources disposed at different input positions in a laieral direction across the input end of the waveguide, the waveguide having first and second, opposed guide surfaces extendin between the input end and the reflective end for guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from the reflective end into respective optical windows in. output directions distributed in. the lateral direction ia dependence on the input positions, wherein the reflective end converges the reflected light such that reflected light from light sources that are offset rom the optical axi of the waveguide fails to illuminate outer portions- of the waveguide, and the directional backligh device further comprises an array of second light sources disposed along each side of the waveguide that extends between the input end and the reflective end and between the guiding surfaces and arranged to supply light to said outer portions of the waveguide:.

[1 1 ] According to a fourth aspect of the present invention, there is provided, a directional display device comprising: a waveguide extending between an input end for receiving input light and a reflective end for reflecting the- input light back through the waveguide; a array of light sources disposed at different input positions across the input end of the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from the reflective end into respective optica! windows in outpirt directions distributed in the lateral direction i dependence 00 the input positions; and a trausraissive spatial light modulator extending across the waveguide for modulating the light output therefrom, wherein, the spatial, light modulator extends across only part, of the area of the waveguide,

[12] According to a fifth aspect of the present invention, there is provided, a backlight apparatus comprising: a directional waveguide extending between an. input end for receiving input light and a reflective end for reflecting the input light back through the directional waveguide, the directional waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding light forwards and back along the directional waveguide, wherein the second guide surface has a plurality of light extraction features feeing the reflective en and arranged to reflect the light guided back through the directional waveguide from the reflective end from different input positions across the input end in different directions through the first guide surface that are dependent on the input position; and an array of light sources arranged to illuminate the directional waveguide at different input positions across the input end of the directional waveguide, wherein the reflective end converges the reflected light such that reflected light from light sources that are offset from the optical axis of the directional waveguide fails to illuminate outer portions of the directional waveguide; a backlight structure arranged extending across the second guide surface of the directional waveguide and arranged to provide illumination through the directional waveguide including the outer portions that fail to be illuminated by offset light sources..

[13] Thus, each of the first to fifth aspects of the present invention provide structures that provide for illumination of the outer portion, of the waveguide that, otherwise fails to be illuminated by light sources. The first to fifth aspects of the present invention may be applied together in any combination.

[14] According to a sixth aspect of the present invention, there is provided, an aniostereoscopic display apparatus, comprising; a display device comprising an array of pixels, the display device bein controllable to direct an. image displayed on all of the pixels int selectable viewing windows having different positions; and a control system that is operable in a 3D mode of operation and a 2D mode of operation, the control system being arranged in th 3D mode of operation to control the display device to display temporally multiplexed left and right images and synchronously to direct the displayed mages into viewing windows in positions in a lateral direction corresponding to the left and right eyes of the observer, and being arranged in the 2D mode of operation to control the display device to display a continuous 2D image, wherein, the display device farther comprises an angle-dependent diffuser film extending across the display device having a property that light incident at angles in a first range around the n rm l to the film in the lateral direction is not angularly diffused bat light incident at angles in a second ramie m the lateral direction outside said first name is angularly diffused.

[15] Furthe according to a sixth aspect of the present invention, there is provided, a waveguide structure comprising; a waveguide extending between an input end for receiving input light and a reflective end for reflecting the input light back through the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from different input positions in a lateral direction across the input end after reflection from the reflective end in output directions distributed in a lateral direction in dependence on the input position; and an angle-dependent diffuser film extending across the waveguide, having a property that light incident at angles in a first range around the normal to the film in the lateral direction is not angularly diffused but light incident at angles in a second ranse in the lateral direction outside said range is angularly diffused.

[16] The diffuser film in accordance with the sixth aspect of the present invention may provide increased viewing angle in a 2D mode of operation at a relatively low cost in an. apparatus that is also capable of providing a 3D mode of operation using a time division multiplexing technique,

[ 17] The sixth aspect of the present invention may be applied in. combination with, any of the first to fifth, aspects of the present invention or with any combination thereof^*

[18] Accordin to a seventh aspect of the present invention, there is provided, a directional illumination apparatus, comprising: an imaging directional backlight for directing light comprising; a waveguide for guiding light, further comprising: a first light guiding surface; and a second light guiding surface, opposite the first light guiding surface; and an illuminator array fo providing light to the imaging directional backlight; and an additional optica! element that alters the optical system of the imaging directional backlight to provide a substantially uniform 2D i 1 lu iB i iiati on mode .

[19] According to an. eighth aspect of the present, invention, there is provided, a stepped imaging directional backlight apparatus, comprising: a stepped waveguide for guiding light, wherein, the waveguide comprises: a first light guiding surface; and a second light guiding surface, opposite the first light guiding surface, the second light guiding surface comprising at least one guiding feature and a plurality of extraction features, wherein the extraction features direct light to exit the stepped waveguide; a first illumination input surface located between the first, and second light guiding surfaces, the first illumination input surface operable to receive light from a first array of light sources; an illuminator array for providing light to the stepped imaging directional backlight; and an additional optical element that alters the optical system of the .stepped, imaging directional backlight to provide a substantially uniform 2D illumination mode.

[20] According to a ninth aspect of the presen invention, there is provided, an

imaging directional backlight, comprising: an input side located at a first end of a waveguide; a reflective side located at a second end of the waveguide; a first light directing side and a second light directing side located between the input side and the reflective side of the waveguide, wherein, the second light directing side further comprises a plurality of guiding features and a plurality of extraction features; and an additional optical element that alters an optical system of the imaging directional backlight to provide a substantially uniform 2D illumination mode, wherein the additional optica! element is at least one of a optical emitter, an imaging facet end, or an alternative light path.

[21] According to a tenth aspect of the present invention,, there is provided, a folded imaging directional backlight system that provides a substantially -uniform 2D illumination mode, comprising: a folded imaging directional backlight, comprising; a first waveguide for guiding light operable to receive light from an illuminator array; and a second waveguide optically connected to the first waveguide and operable to receive light from the illuminator array, wherei the first waveguide has a first edge with edge facets and die second waveguide has a second edge with edge facets, further wherein, the edge facets provide a substantially uniform 2D illumination, mode. [22 ] Any of the aspects of the present invention may be applied in an combination.

[23] Embodiments herein may provide a autostereoscopic displa that provides wide angle viewing which may allow for directional viewing and conventional 2D compatibility. The wide angle viewin mode may be for observer tracked autostereoscoptc 3D display, observer tracked 2D display (for example for privacy or power saving applications), for wide viewing angle 2D display or for wide viewing angle stereoscopic 3D display. Further, embodiments may provide a controlled illuminator for the purposes of an efficient autostereoseopic display. Such components ca be used in directional backlights, to provide directional, displays including autostereoscopic displays. .Additionally* embodiments may relate to a directional, backlight apparatus and a directional display which may incorporate the directional backlight apparatus. Such an apparatus may be used for autostereoscopic displays, privacy displays, multi-user displays and other directional display applications.

[24] in embodiments, the optical function of the directional backlight can he provided by a multiple imaging direction backlight system in which side voided regions of end illuminators may be filled. Advantageously such an. arrangement may provide optical functions in addition to the respective optical valve functions while preserving the advantages of high efficiency, large back working distance and thin form factor of the respective optical valve.

[25] Embodiments herein may provide an autostereoscopic displa with large area and thin structure. Further, as will be described, the optical valves of the present disclosure may achieve thin optical components with large back working distances. Such components can be used in directional backlights, to provide directional displays including autostereoscopic. displays. Further, embodiments may provide a controlled, illuminator for the purposes of an efficient autostereoscopic display.

[26] Embodiments of die present disclosure may be used in a variety of optical systems. The embodiment may include or work with a variety of projectors, projection systems, optical components, displays, icrodisplays, computer systems, processors, self-contained projector systems, visual and/or audiovisual systems and electrical and/or optical devices. Aspects of the present disclosure may be used with practically any apparatus related to optical and electrical devices, optical systems, presentation systems or any apparatus that ma contain any type of optical system. .Accordingly, embodiments of the present disclosure may be employed in optical systems, devices used in visual and/or optica! presentations, visual peripherals and so on and in a number of cotnputing envin menis.

[27] Before proceeding to the disclosed embodiments in detail, it should be understood that the disclosure is not limited in its application or creation to the details of the particular arrangements shown, because the disclosure is capable of othe embodiments, Moreover, aspects of the -disclosure may be set forth in different combinations and arrangements to define embodiments unique in their own right:. Also, the terminology used herein is for the purpose of description and not of limitation.

[28] Directional backlights offe control over the illumination emanating from substantially the entire output surface controlled typically through modulation of independent LED Sight sources arranged at the input aperture side of an optical waveguide. Controlling the emitted light directional distribution can. achieve single person viewing for a security function, where the display can only be seen by a single viewer from a limited range of angles; high electrical efficiency, where illumination is only provided over a small angular directional distribution: alternating left and right eye viewing for time sequential stereoscopic and autostereoscopic display; and low cost.

[29] These and other advantages and features of the present disclosure will become apparent to those of ordinary skill in the art upon, reading this disclosure in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[30] Embodiments are illustrated by way of example in the accompanyin FIGURES, i which like reference numbers indicate similar parts, and in which:

[31] FIGURE 1A is a schematic d iagram illustrating a front view of light propagatio in. one embodiment of a directional display device, in accordance with the present disclosure;

[32] .FIGURE IB is a schematic diagram illustrating a side view of light propagation i one embodiment of the directional display device of FIGURE I A, m accordance with the present disclosure;

[33] FIGURE 2A is a schematic diagram illustrating in a top view of light propagation in another embodiment of a directional display device, in accordance with the present disclosure; [34] FIGURE- 2B is a schematic diagram illustrating light propagation m a front: view of the directional display device of FIGURE 2A_S in accordance with the present disclosure;

[35] FIGURE 2C is a schematic diagram illustrating light propagation in a side view of the directional display device of FIGURE 2A, in accordance with the present disclosure;

[36] FIGURE 3 is a schematic diagram illustrating in. a side view of a directional displa device, in accordance with the present disclosure;

[37] FIGURE 4A Is schematic diagram illustrating in a .front view, generation of a viewin window in a directional display device including curved light extraction, features,, in. accordance with the present disclosure;

[38] FIGURE 4B Is a schematic diagram illustrating in a front view, generation of a first and a second viewing window in a directional display device including curved light extraction features, in accordance with the present disclosure;

[39] FIG URE 5 is a schematic diagram illustrating generation of a first viewing window in a directional display device including linear light extraction features, in accordance with die present disclosure;

[40] FIGURE 6 A i a schematic diagram illustrating one embodiment of the generation of a first viewing window in a time multiplexed directional display device in a first time slot _» in accordance with the present disclosure;

[ 1 ] FIGURE€B is a schematic diagram i Oustraiing another embodiment of the generation of a second viewing window in a time multiplexed, directional display device in a second time slot, in accordance with the present disclosure;

[42] FIGURE 6C is a schematic diagram illustrating another embodimen of the generation of a first and a second viewing window in a time multiplexed directional display device, in accordance with the present disclosure;

[43] FIGURE 7 is a schematic diagram illustrating an observer trackin autostereoscopic directional display device, in accordance with the present disclosure;

[44] FIGURE 8 is a schematic diagram illustrating a multi-viewer directional display device, in accordance with the present disclosure;

[45] FIGURE 9 is a schematic diagram illustrating a privacy directional displa device, in accordance with the present disclosure; [46] FIGURE 1.0 is a schematic diagram illustrating in side view, the structure .of a time multiplexed directional display device, in accordance with the present disclosure

[47] FIGURE 11 A is a schematic diagram illustrating a directional display apparatus comprising a directional display device and a control system, in accordance with the present disclosure;

[48] FIGURE !IB is a schematic diagram illustrating a left side region of ^'insufficient illumination for right sided off-axis viewing of a. directional backlight* in accordance wit the present disclosure;

[49] FIGURE I2A is schematic diagram illustrating a right side region of insufficient illumination for left sided off-axis viewing of a directional backlight, in accordance with the present disclosure;

[50] FIGURE 12B is a schematic diagram illustrating the top view of a directional backlight arranged to reduce the visibility of the void, outer portions, in accordance with the present disclosure;

[51] FIGURE 12C is a schematic diagram illustrating a directional display device comprising a directional backlight and spatial light, modulator of area outside the outer regions achieved by edge light sources, in accordance with the present disclosure;

[52] FIGURE 12B is a schematic diagram illustrating a directional display device comprising a directional backlight and spatial light modulator of area outside the outer regions achieved by edge ligh sources wherein the directional backlight is tapered, in accordance with the present disclosure;

[53] FIGURE 13A is a schematic diagram illustrating a directional backiight comprising a waveguide that has polished transmitting edges to direct light into voided regions between pairs of sources while allowing unwanted rays to exit the guide, in accordance with the present disclosure;

[54] FIGURE 13B is a schematic diagram illustrating a directional backlight comprising a waveguide that has polished transmitting edges to direct light into voided regions between pairs of sources while allowing unwanted rays to exit die guide, in accordance wit the present disclosure; [55] FIGURE- 14A is a schematic diagram illustrating operation of a. directional backlight with paired sources for increased illumination areas, in accordance with the present disclosure;

[56] IGURE 14B is a schematic diagram illustrating operation of a directional backlight with paired sources for increased illumination areas, in accordance with the present disclosure:

[57] FIGURE 14C is a schematic diagram illustrating operatio of a directional backlight with paired sources for increased illumination areas, in accordance with the present disclosure;

[58] FIGURE 15 is a schematic diagram illustrating an embodiment comprising a control system, a light source array and a directional waveguide comprising reflective sides arranged to achie ve filling of void outer regions formed by a first light source by illuminating a second ligh t source, in accordance with the present disclosure;

[59] FIGURE 16A is a schematic diagram illustrating a top view of a directional display device comprising a stepped waveguide, in accordance with the present disclosure;

[60] FIGURE Ϊ6Β is a schematic diagram illustrating a top view of a directional display device comprising a stepped waveguide, in accordance with the present disclosure;

[61] FIGURE 16C is a schematic diagram illustrating a top view of a directional display device comprising a non-collimating reflecting end, in accordance with the present disclosure;

[62] FIGURE 160 is a schematic diagram illustrating a top view of a directional display device comprising a stepped waveguide, in accordance with the present disclosure;

[63] FIGURE Ϊ6Ε Is a schematic illustration of the front view of a directional display apparatus comprising outer strings of light sources, in accordance with the present disclosure;

[64] FIGURE Ϊ7Α is a schematic illustration of two artefacts which ma appear at the edge of the viewing region of a directional display apparatus- on one side, in accordance with the present disclosure;

[65] FIGURE 17B is a schematic illustration of two artefacts which may appear at the edge of the viewing region of the directional display apparatus o the opposite side to FIGURE 17 A, in accordance wit the present disclosure;

[66] FIGURE 17C is a schematic illustration of one method for compensating the appearance of the void portion of a directional display apparatus, In accordance with, the present disclosure; [67] FIGURE- 17B is a schematic illustration of a further method for compensating the appearance of the void, portion of a directional display apparatus, in accordance with the present disclosure;

[68] FIGURE 17E is a schematic illustration of a further method for compensating the appearance of the void portion of directional display apparatus, in accordance wit the present disclosure;

[69] FIGURE ISA is a schematic diagram illustrating an directional backlight in which side reflecting facets are introduced to redirect light into voided regions of a directional backlight system, in accordance with the present disclosure;

[70] FIGURE I SB is a schematic diagram illustrating a further directional backlight in which side reflecting facets are introduced to redirect light into voided regions of a directional backlight system, in accordance with the present disclosure;

[71] FIGURE ISC is schematic diagram illustrating yet another farther directional backlight in which side reflecting .facets are introduced to redirect light into voided regions of a directional backlight system, in accordance with the present disclosure;

[72] FIGURE 19 is a schematic diagram illustrating a further directional backlight in which side holographic films redirect light into voided regions of a directional backlight system, in accordance with die present disclosure;

[73] FIGURE 2ΘΑ is a schematic diagram illustrating a directional backlight in which additional light sources are used to introduce light into the side of an optical valve, in accordance with the present disclosure;

[74] FIGURE 20B is a schematic diagram illustrating another directional backlight in which additional l g t sotirces are used to introduce light into the side of art optical valve, in accordance with the present disclosure;

[75] FIGURE 2-0C is a schematic diagram illustrating another directional backlight in whic additional light sources are used to introduce light into the side of an optical valve, in accordance with the present disclosure;

[76] FIGURE^' 21 is a schematic diagram illustrating another directional backlight in which local arrays of sources launch light at controlled angles for wide angle uniform viewing with independent window control, in accordance with the present disclosure; [77] FIGURE 22A is a schematic diagram illustrating a further directional backlight in which a backlight is placed adjacent an optical valve, in accordance with the present disclosure;

[78] FIGURE 22 B is a schematic diagram illustrating a further directional backlight in which a backlight is placed, adjacent an optical valve, in accordance with the present disclosure;

[79] FIGURE 22C is a schematic diagram illustrating a further directional backlight in which a backlight is placed adjacent an optical valve, in accordance with the present disclosure;

[80] FIGURE- 23 is a schematic diagram illustrating a further directional backlight in which a source array is altered in position ^'between adjacent backlights, in accordance with the present disclosure;

[81] FIGU RE 24 is a schematic diagram illustrating an directional backlight in which light is switched between illuminating backlight systems, in accordance with the present disclosure;

[82] FIGURE 25A is schematic diagram illustrating a directional display device whereby a angle dependent diffuser is used to diffuse high angle rays to a greater extent than those directed normally from ie imaging directional backlight in accordance with the present disclosure;

[83] FIGURE 25B is a schematic diagram illustrating a side view of an angular dependent diffuser, in accordance with the present disclosure;

[84] FIGURE 25C is a schematic diagram illustrating a side view of an angular dependent diffuser, in accordance with the present disclosure;

[85] FIGURE 25D is a schematic diagram illustrating an arrangement of an angular dependent diffuser in an autostereoscopic directional display device arranged to provide wide angle viewing, in accordance with the present disclosure;

[86] FIGURE 26 is a schematic diagram illustrating a directional backlight in which illuminating light is diffused using a swiichabS.e diffusing, element, in accordance with the present disclosure;

[87] FIGURE 27 is a schematic diagram illustrating a directional backlight in which guided light may be extracted in a diffuse form b optically contacting the bottom surface of a directional backlight with a diffuse reflecting element, in accordance with the present disclosure;

[88] FIGURE 28 is a schematic diagram ilh.isirati.ng a directional backlight -in which guided light may be extracted in a diffuse form by optically contacting the bottom surface of the directional acklmht with a diffuse refleetins element through el ctro&nmna material -surface material, accordance with the present disclosure:

[89] FIGURE 29 is a schematic diagram illustrating a directional, backlight in which electro- wetting material is made to move from behind reflecting facets into the guiding region of an imaging directional backlight forcing light to exit and reflect off a diffusing surface, In accordance wit the present disclosure;

[90] FIGURE 36 is a. schematic illustration of a top view of a wedge directional backlight arranged to achieve reduced visibility of void portions, in accordance with the present -disclosure; and

[ 1] FI U E 31 is schematic illustration of the side view of a wedge directional backlight, in accordance with the present disclosure.

DETAILED DESCRIPTION

[92] Time multiplexed autostereoscopic displays can advantageously improve the spatial resolution of autostereoscopic display by directing light from all of the pixels of a spatial S ight modulator to a first viewing windo in a first time slot, and all of the pixels to a second viewing window in a second time slot. Thus an observer with eyes arranged to receive light in first and second viewing windows will see a full resolution image across the whole of the display over multiple time slots. Time multiplexed displays can advantageousl achieve directional illumination by directing an illuminator arra through a .substantially transparent time multiplexed spatial light modulator rising directional optica! elements, wherei the directional optical elements substantially form an image of the illuminator array in the window plane.

[93] The imif rmity of the viewing windows may be advantageously independent of the arrangement of pixels in the spatial light modulator. Advantageously, such displays can provide observer tracking displays which have low flicker, with low levels o cross talk for a moving observer.

[94] To achieve high uniformity in- the window plane, it is desirable to provide a array of illumination elements that have a high spatial uniformity. The il l uminator elements of the time sequential illumination system may be provided, for example, by pixels o a spatial, light .modulator with size approximately 1.00 micrometers in combination with, a lens array. However, such pixels suffer from similar difficulties as for spatially multiplexed displays. Further, such devices may have low efficiency and higher cost, requiring additional display components.

[95] High window plane uniformity can be conveniently achieved with macroscopic illuminators, for example, an array of LEDs in combination with homogenizing and diffusing optical elements that are typically of size 1 mm or greater. However, the increased size of the il!umiuator elements means that the size of the directional optical elements increases proportionately. For example, a 16 mm wide illuminator imaged to a 65 mm wide viewin window may require a 20(3 mm. back working distance. Thus, the increased thickness of the optical elements can prevent useful application, for example, to mobile displays, or large area displays.

[96] Addressing the aforementioned shortcomings, optical valves as described in commonly- owned U.S. Patent Application No. .13/300,293 advantageously can be arranged in combinatio with fast switching transmissive spatial light modulators to achieve time multiplexed autostereoscopic illumination in a thin package while providing high resolution images with flicker free observer tracking and low levels of cross talk. Described is a one dimensional array of viewing positions, or windows, that can display different images in a first, typically horizontal, direction, but contain the same images when moving in a second, typically vertical, direction.

[97] Conventional .non-imaging display backlights commonly employ optical waveguides and have edge illumination from light sources such as LEDs. However, it should be appreciated that there are many fundamental differences in the function, design, structure, and operation between such conventional non-imaging display backlights and the imaging directional backlights discussed in the present disclosure,

[98] Generally, for example, in accordance with the present disclosure^ imaging directional backlights are arranged to direct, the illumination from multiple light sources through a display panel to respective multiple viewing windows in at least one axis. Each viewing window is substantially formed as an image in at least one axis of a light source by the imaging system of the imaging directional backlight. An imaging system ma he formed between multiple light sources and the respective window images. In this manner, the light from each of the multiple light sources s substantially not visible for an observer ^'s eye outside of the respective viewin window.

[99] In contradistinction, conventional non-imaging backlights or light guiding plates (LGPs) are used for illumination of 2D displays. See, e,g,, Kaiil Kalantar et al... Backlight Urn! With Double Surface Light Emission, J. Soc. Inf Display, Vol 12, Issue 4, pp. 379-387 (Dec. 2004). Non-imaging backlights are typically arranged to direct the illumination from multiple- light sources through display panel into a substantially common viewing zone for eac of the multiple light sources to achieve wide viewing angle and high displa uniformity. Thus nonimaging backlights do not form viewing windows. In this manner* the light, from each of the multiple light sources may be visible for an observer's eye at substantially all positions across the viewing zone. Such conventional nonimaging backlights may have some directionality, for example, to increase screen gai compared to Lambertian illumination, which .may be provided by brightness enhancement films such as BEF^L from 3M However, such directionality may be substantiall the same for each of the respecti ve light sources. Thus, for these reasons and others that should be apparent to persons of ordinary skill, conventional non-imaging backlights are different to imaging directional backlights. Edge lit non-imaging backlight illumination structures may be used in liquid crystal display systems such as those seen in 2D Laptops, Monitors and TVs. Light propagates .from the edge of a lossy waveguide which .may include sparse features; typically local indentations in the surface of the guide which cause light to be lost regardless of the propagation direction of the light.

[100] As used herein, an optical valve is an optical structure that may be type of light guiding structure or device referred, to as, for example, a light valve, an optical valve directional backlight, and a valve direciional backlight f'v-DBL"). In. the present disclosure, optical valve is different to a spatial light modulator (even though spatial light modulators may be sometimes generally referred to as a "light valve" in the art). One example of an imaging directional backlight is an optical valve that may employ a folded optical system. Light may propagate substantially without loss in one direction through the optical valve, may be incident on an imaging reflector, and may counier-propagate such that the light may be extracted by reflection off tilted light extraction features, and directed to viewing windows as described in US Pat. App. Ser. No. 13/300,29.1, which is herein incorporated by reference in its entirety. [10.1 ] Additionally, as used herein, a stepped waveguide imaging directional backlight may be at least one of an. optical valve, A stepped waveguide is a waveguide for m imaging directional backlight comprising a waveguide for guiding light, further comprising; a first light guiding surface; and a second light guiding surface, opposite the first light guiding surface, further comprising a plurality of light guiding features interspersed with a plurality of extraction features arranged as steps.

[102] hi operation, light may propagate within an exemplary optical valve in a first direction from an input side to a reflective side and may be transmitted substantially without toss. Light may be reflected at the reflective sid and propagates in a second direction substantially opposite the first direction. As the light propagates in. the second direction, the Sight may be incident on light extraction features, which are operable to redirect the light outside the optical valve. Stated differently, the optical valve generally allows light to propagate i the first direction and may allow light to be extracted, while propagating in the second direction.

[103] The optical valve may achieve time sequential directional illumination, of large display areas. Additionally, optica! elements may be employed that are thinner than the back working distance of the optical elements to direct light from macroscopic illuminators to a window plane. Such displays may use a arra of light extraction features arranged to extract: Sight counter propagating in a substantially parallel waveguide.

[ 104] Thin imaging directional backsight implementations for use with LCDs have been proposed and demonstrated by 3M, for example U.S. Paten Mo, 7,528,893; by Microsoft, for example U.S. Patent No, 7,970,246 which, may be referred to herein as a "wedge .type directional backsight;" by ealD, for example U.S. Patent Application No. 13/300,293 which may be referred to herein as an. "optical valve" or "optical valve directional, backlight ". all of which ar herein incorporated by reference in their entirety .

[105] The present disclosure provides stepped waveguide imaging directional backlights in which light ma reflect back and fort between the internal faces of, for example, a stepped waveguide which may include a first side and a first set of features. As the light travels along the length of the stepped waveguide, the light may not substantially change angle of incidence with respect to the first side and first set of surfaces and so may not reach the critical angle of the medium at these internal faces,. Light extraction, .may be advantageously achieved by a second set of surfaces (the step "risers") that are inclined to the .first set of surfaces (the step "treads"). Note that the second set of sur faces ma not he part of the light guiding operation of the stepped waveguide, but may be arranged to provide light extraction, from the structure. By contrast, a wedge type imaging directional backlight may allow light to guide within a wedge profiled waveguide having continuous internal surfaces., The optical valve is thus not a wedge type imaging directional backlight

[106] FIGURE 1A is a schematic diagram illustrating a front view of light propagation in one embodiment of a directional display device, and FIGURE I B is a schematic diagram illustrating a side view of light propagation in the di rectional display devi ce of FIGURE I A.

[ 107] FIGURE ΪΑ illustrates a front, view in the xy plane of a directional backlight of a directional display device, and includes an illuminator arra 15 which may be used to illuminate a stepped waveguide 1. Illuminator array .15 includes illuminator elements 15a through illuminator element ISn (where n is an integer greater than one), in one example, the stepped waveguide 1 of FIGURE 1 A may he a stepped, display sized waveguide I_* Illumination elements 15a through ISn are light sources that may be light emitting diodes (LEDs). Although LEDs are discussed herein as illuminator elements 15a - 15n, oilier light sources may be used such as, but not. limited to, diode sources, semiconductor sources, laser sources, local field emission sources, organic emitter arrays, and so forth. Additionally, FIGURE I B illustrates a side view in the z plane, and includes illuminator array 15, SLM 48, extraction features 12, guiding features 1.0, and stepped waveguide 1 , arranged as shown. The side view provided in FIGURE 18 is an alternative view of the front view shown in FIGURE 1 A. Accordingly, the illuminator array IS of FIGU RES 1 A and IB corresponds to one another and the stepped waveguide 1 of FIGURES 1A and IB may correspond to one another,

[ 108] Further, in FIGURE I B, the stepped waveguide I may have an input end 2 that is thin and a reflective end 4 that is thick. Thus the waveguide 1 extends between the input end 2 that receives input light and the reflective end 4 that reflects the input light hack through the waveguide 1 , The length of the input end 2 in a lateral direction across the waveguide is greater than the height of the input end 2. The Illuminator elements 1.5a - - 1.5η. are disposed at different input positions in a lateral direction across the input end 2. [109] The waveguide .1 has first and second, opposed guide surfaces extending between the input end 2 and the reflective end 4 for guiding light forwards and back along the waveguide t.

The second guide surface has a plurality of light extraction features 12 facing the reflective end 4 and arranged to reflect at least some of the light guided back through the waveguide I from the reflective end from different input positions across the input end in different directions through the first guide surface that are dependent on the input position.

[1 10] In this example, the light extraction, features 12 are reflective facets, although other reflective features coiild be used. The riant extraction features 12 do not guide Haht throuah the waveguide, whereas the intermediate regions of the second, guide surface intermediate the light extraction features 12 guide light without extracting it. Those regions of the second guide surface are planar and may extend, parallel to the first guide surface, or at a relatively low inclination. The light extraction features 12 extend laterally to those regions so that the second guide surface has a stepped shape which may include the light extraction features 12 and. intermediate regions. The light extraction features 12 are oriented to reflect light from the light sources, after reflection from the reflective end 4, through the first guide surface.

[I l l J The light extraction features 12 are arranged to direct input ligh from different input positions in the lateral direction across the input end in different directions relative to the first guide surface that are dependent on ihe input position. As the illumination elements 15a- I Sn are arranged .at different input positions, the light from respective illumination elements 15a~15n is reflected in those different directions. In this manner, each of the illumination elenieots i Sa-1.5n directs light into a respective optical window in output directions distributed in the lateral direction in dependence on the input positions. The lateral direction across the input end 2 in which the input positions are distributed corresponds wit regard to the output light to a lateral direction to the normal to the first guide surface. The lateral directions as defined at the input end 2 and with regard to the output light remain parallel i this embodiment where the deflections at the reflective end 4 and the first guide surface are generall orthogonal to the lateral direction.. Under the control of a control system, the illuminator elements 15a - 1.5n may be selectively operated to direct light into selectable optical window. The optical windows may be used individually or in groups as viewing windows. [ 1 12] The SLM 48 extends across the waveguide and modulates the light output therefrom. Although, the SLM 48 ma a. liquid crystal display (LCD), this is merely by way of example and oilier spatial light modulators or displays may be used including LCOS, DLP devices, and so forth, as this illuminator may work in reflection, in this example, the SLM 48 is disposed, across the first guide surface of the waveguide and rn.odui.ates the light output through the first guide surface after reflection from the light extraction features 12,

[ 1 13] The operation, of a directional display device that .may provide a one dimensional array of viewing windows is illustrated in front view in .FIGURE 1 A, with its side profile shown in FIGURE I B, in operation, in FIGURES 1 A and IB,, light may be emitted from an illuminator array 15, such as an array of illuminator elements 15a through 15n, located at different positions, y, along the surface of thin end side 2, x=0, of the stepped waveguide 1. The light may propagate along -fx in a. first direction, within the stepped waveguide 1 , while at the same time, the light may fan out in the xy plane and upon reaching the far curved end side 4, may substantially or entirely till the curved end side 4. While propagating, the light may spread out to a set of angles in the xz plane up to, but not exceeding the critical angle of the guide material. The extraction features 12 that link the guiding features 10 of the bottom side of the stepped waveguide I may have a tilt angle greater than the critical angle and hence may be missed by substantially all light propagating along fx in the first direction., ensuring the substantially lossless forward propagation.

[ 14] Continuing the discussion of FIGURES 1 A and 1 B, the curved end side 4 of the stepped waveguide 1 may be made reflective, typically by being coated with a . reflective materia! such as, for example, silver, although other reflective techniques may be employed.. Light may therefore be redirected in. a second direction, hack down the guide in the direction of x and may be substantiall collimated in the .xy or display plane. The angular spread may be substantially preserved in the xz plane about the principal propagation direction, which may allow light to hit the riser edges and reflect out of the guide. In an embodiment with approximately 45 degree tilted extraction features 12, light may be effectively directed approximately normal to the xy display plane with the xs angular spread substantially maintained relative to the propagation direction. This angular spread may be increased when light exits the stepped waveguide I through .refraction, but may be decreased somewhat dependent on the reflective properties of th extraction features 12.

[I IS] -fo some embodiments with uncoafced extraction features 12. reflection ma be reduced when total internal reflection (TIR) fails, squeezing the AT angular profile and shifting off normal. However, in other embodiments having silver coated or metallized extraction features, the increased angular spread and centra! normal direction may be preserved. Continuing the description of the embodiment with silver coated extraction, features, in the plane, light may exit the stepped waveguide 1 approximately eoMimated and may be directed off normal in proportion to the y-positton of the respective illuminator element 15a - I5n in illuminator array 15 from the input edge center. Having independent illuminator elements 1 5a - 15n along the input edge 2 then enables light to exit from the entire first light directing side 6 and propagate at different external angles, as illusirated in FIGURE 1 A.

[ 1 16] Illuminating a spatial light modulator (SLM) 48 such as a fast, liquid crystal display (LCD) panel with such a device may achieve autostereoscopic 3D as shown In top view or yz~ plane viewed from the illuminator array 15 end in FIGURE 2 A, front view in FIGURE 2B and side view hi FIGURE 2C. FIGURE 2A is a schematic diagram illustrating in a top view, propagation of light in a directional display device, FIGURE 2B is a schematic diagram illustrating in a front view, propagation of light in a directional display device, and FIGURE 2C is a schematic diagram illustrating in side view propagation, of light in. a directional display device. As illustrated in FIGURES 2A, 2B, and 2C, stepped waveguide 1 ma be located behind fast (e.g.. greater than 1.00Hz) LCD panel SLM 48 that displays sequential right and left, eye images, in synchronization, specific illuminator elements 15a through I5n of illuminator array .15 (where n is an integer greater than one) may be selectively turned on and off, providing illuminating light that enters right and left eyes substantially independently by virtue of the system's directionality. In the simplest case, sets of illuminator elements of illuminator array 1.5 are turned on together, providing a one dimensional viewing window 26 or an optical upil with limited width in the horizontal direction, but extended in the vertical direction, in which both eyes horizontally separated ma view a left eye image, and another viewing window 44 in which a right eye image may primarily be viewed by both eyes, and a central position in which both the eyes may view different images,. In this way_* 3D .may he viewed when the head of a viewer is approximately centrally aligned. Movement to the side away from the central position may result in the scene collapsing onto a 2D image.

[11.7] The reflective end 4 may have positive optical power in the lateral direction across the waveguide. In embodiments in which typically the reflective end 4 has positive optical power, the optical axis may be defined with, reference to the shape of the reflective end 4, for example being a line that passes through the centre of curvature of the reflective end 4 and coincides with the axis of reflective symmetry of the end 4 about the x-axis. In the case that the reflecting surface 4 is flat, the optical axis may he similarly defined with respect to other components having optical power, tor example the light extraction features 12 if they are curved, or the Fresnei lens 62 described below. The optical axis 238 is typically coincident with the mechanical axis of the waveguide I .In the present embodiments that typically comprise a substantially cylindrical reflecting surface at end 4, the optical axis 238 is line thai passes through the centre of curvature of the surface at end. 4 and coincides with the axis of reflective symmetry of the side 4 about the x-axis. The optical axis 238 is typically coincident with the mechanical axis of the waveguide 1. ^'the cylindrical reflecting surface at end 4 may typically comprise a spherical profile to optimize performance for on-axis and off-axis viewing positions. Other profiles ma be used.

[118] FIGURE 3 is a schematic diagram illustrating in side view a directional display device. Further, FIGURE 3 illustrates additional detail of a side view of the operation of stepped waveguide 1. which may be a. transparent material. The stepped waveguide 1 may include an illuminator input side 2, a reflective side 4, a first light directing side 6 which may be substantiall planar, and a second light directing side 8 which includes guiding features 10 and light extraction features 12., In operation, light rays 16 -from an illuminator element 15c of an illuminator array 1.5 (not. shown in FIGURE 3), that may be an addressable array of LEDs for example, may be guided in. the stepped waveguide I. by means of total internal reflection by the first light directing side and total internal reflection by the guiding feature 10, to the reflective side 4, which may be a mirrored surface. Although reflective side 4 may be a mirrored surface and may reflect light, it may in some embodiments also be possible for light, to pass through reflective side 4, [ 1 19] Continuing the discussion of FIGURE 3, light ray 18 reflected by the reflective- side 4 may be further guided in. the stepped, waveguide I by total internal reflection, at the reflective side 4 and may be reflected by extraction features 12. Light rays 18 that are incident on extraction features 12 may be substantially deflected away from guiding modes of the stepped waveguide I and ma be directed, as shown by ray 20, through the side 6 to an optical pupil that may form, a viewing window 26 of an autostereoscopic display. The widt of the viewing window 26 may be determined by at least the size of the illuminator_* output design, distance and optical power i the side 4 and extraction features 12. The height of the viewing window ma be primarily determined by the reflectio cone angle of the extraction, .features 12 and the illumination cone angle input at the input side 2. Thus each viewing window 26 represents a range of separate output directions with respect to the surface normai direction of the spatial light modulator 48 that intersect with a plane at the nominal viewing distance,

[120] FIGURE 4A is a schematic diagram illustrating in front view a directional display device which may be .illuminated by a first illuminator element and including curved light extraction features. Further, FIGURE 4A shows in front view further guiding of Sight rays from illuminator element 15c of illuminator array 15, in the stepped waveguide i . Each of the output rays are directed towards the same viewing window 26 from the respective illuminator 14. ^'Thus light ra 30 may intersect the ray 20 in the window 26, or may have a different height in the window as shown by ray 32, Additionally , in various embodiments, sides 2:2, 24 of die waveguide 1 may be transparent, mirrored, or blackened surfaces. Continuing the discussion of FIGURE 4A, light extraction features 12 may be elongate, and the orientation of light extraction features 12 in a first region 34 of the light directing side 8 (light directing side 8 shown in FIGURE 3, but not shown in FIGURE 4A) ma be different to the orientation of light extraction features 12 in a second region 3 of the light directing side 8.

[121] FIGURE 4B is a schematic diagra illustrating in. front view an optica! valve which ma illuminated by a second illuminator element. Further, FIGURE 4B shows the light rays 40, 42 from a second illuminator element 15h of the illuminator array 15. The curvature of the reflective end on the side 4 and the light extraction features 12 cooperatively produce a second viewing window 44 laterally separated from the viewing window 26 with light rays from the illuminator element 15h. [1221 Advantageously, the arrangement illustrated in FIGURE 4B may provide a real image of the illuminator element 15c at a viewing window 26 in which the real image may be formed by cooperatioii of opticai power in reflective side 4 and opticai power which may arise from different orientations of elongate light extraction features J 2 between regions 34 and 36. as shown in FIGURE 4 . The arrangement of FIGURE 4B may achieve improved aberrations of the imaging of illuminator element 15c to lateral positions in viewing window 26. Improved aberrations may achieve an extended viewing .freedom for aft autostereoscopic display while achieving low cross talk levels.

[123] FIGURE 5 is a schematic diagram illustrating in. front view an embodiment of a directional display device having substaotiaily linear light extraction features. Further, FIGURE 5 shows a similar arrangement of components to FIGURE 1 (with corresponding elements being similar), with one of the differences being that the light extraction features 12 are substantially linear and parallel to each other. Advantageously, such an arrangement may provide substantially uniform illumination across a display surface and may be mote convenient to manufacture than the curved extraction features of FIGURE 4A and FIGURE 4B,

[124] FIGURE 6A is a schematic diagram illustrating one embodiment of the generation of a first viewing window in a time multiplexed imaging directional display device in a first time slot, FIGURE 6B is a schematic diagram illustrating another embodiment of the generatio of a second viewing window in a time multiplexed imaging directional: backlight apparatus in a second time slot, and FIGURE 6C is a schematic diagram illustrating another embodiment of the generation, of a first and second viewing window in a time multiplexed imaging directional display device. Further, FIGURE 6A. shows schematically the generation of illumination window 26 .from stepped waveguide 1, Illuminator element group 31 in illuminator array 15 may provide a light cone 17^' directed towards a viewing window 26. FIGURE 6B shows schematically the generatio of illumination window 44, Illuminator^' element group 33 in illuminator arra 15 may provide a light cone 19 directed towards viewing window 44. In cooperation with a time multiplexed display, windows 26 and 44 may be provided in. se uence as sho w In FIGURE 6C_* if the image on a spatial light modulator 48 (not shown in. FIGURES 6A, 68, 6C) is adjusted in correspondence with the light directio output, then an autostereoscopic image may be achieved for a suitably placed viewer. Similar operation, can be achieved with all the directional backlights described herein.. Note that illuminator element groups 31 , 33 each include one or more illumination elements from illumination, elements 1 a. to 15η,,, where n is an integer greater than one.

[125] FIGURE 7 is a. schematic diagram ilhistrating one embodiment of an observer tracking auiostereoscopic directional, display device. As shown in FIGURE ?., selectively turning on and off illuminator elements 15a to 15n along axis 2 provides for directional control of viewing windows. The head 45 position may he monitored with a camera, motion sensor, motion, detector, or any other appropriate optical., mechanical or electrical means, and the appropriate illuminator elements of illuminator arra 15 may be turned on and off to provide substantially independent images to each eye irrespective of the head 45 position. The head tracking system (or a second head tracking system.) may provide monitoring of more than one head 45, 47 (head 47 not shown in FIGURE 7) and may supply the same left and righ eye images to each viewers' left and right eyes providing 3D to all viewers. Again similar operation can he achieved with all the directional backlights described herein.

[ 126] FIGURE 8 is a schematic diagram illustrating one embodiment of a multi-viewer directional display device as an example including an imaging directional backlight. As shown in FIGURE 8, at least two 2D images may be directed towards a pair of viewers 45, 47 so that each viewer may watch a different image on the spatial light modulator 48. The two 2D images of FIGURE 8 may be generated in a similar manner as described with respect to FIGURE 7 in that the two images would be displayed in. sequence and. in synchronization with sources whose light is directed toward the two viewers. One image is presented on the spatial light modulato 48 in a first phase, and. a. second image is presented on the spatial light modulator 48 in a second phase different from the first phase., in correspondence with the first and second phases, the output illumination is adjusted to provide first and second viewing windows 26, 4 respectively. An observe with both eyes In windo 26 will perceive a first imag while an observer with both eyes in window 44 will perceive second image,

[127] FIGURE is a schematic diagram illustrating a privacy directional display device which includes an imaging directional backlight. 2D display systems may also utilize directional backlighting for security and. efficiency purposes i which, light may be primaril directed at the eyes of a first viewer 45 as shown in. FIGURE 9. Further, as illustrated in FIGURE 9, although first viewer 45 may be able to view an image on device 50, light is aot directed towards second viewer 47. Thus second viewer 47 is prevented .from viewing an image on. device 50: Each of the embodiments of the present disclosure may advantageously provide autostereoscopic, dual image ot privacy display functions.

[128] FIGURE 10 is a schematic diagram illustrating in side view the structure of a time multiplexed directional display device as an example including an imaging directional backlight. Further, FIGURE .10 shows in side view an autostereoscopic directional displa device, which may include the stepped waveguide 1 and a Fresnel lens 62 arranged to provide the viewing window 26 in a window plane 106 at a nominal viewing distance from the spatial light modulator for a substantially collimated output across the stepped waveguide ! output surface. A vertical diffuser 68 may be arranged to extend the height of the window 26 further. The light may then be imaged through the spatial. Sight modulator 48. The illuminator array 15 may include light emitting diodes (LEDs) that may, for example, be phosphor converted blue LEDs, or may be separate RGB LEDs, Alternatively, the illuminator elements in illuminator array 15 may include a uniform light source and spatial light modulator arranged to provide separate illumination regions. Alternatively the illuminator elements may include laser light source(s). The laser output may be directed onto a diffuser by means of scanning, for example, using a gaivo o MEMS scanner- in. one example, laser light ma thus be used to provide the appropriate illuminator elements in illuminator array 15 to provide a substantially uniform light source with the appropriate output angle, and further to provide reduction in speckle. Alternatively, the illuminator array 1.5 may be an array of laser light emitting elements. Additionall in one example, the diffuser may be a wavelength converting phosphor, so that illuminatio may be at a different wavelength to the visible output light.

[ 129] A further wedge type directional backlight is generally discussed by U.S. Patent ^'No. 7,660,047 which is herein Incorporated by reference in its entirety. The wedge type directional backlight and optical valve further process light beams in different ways. In the wedge type waveguide, light input at an appropriate angle will output at a defined position on a major surface, but light rays will exit at substantially the same angle and substantiall parallel to the major surface. By comparison, light input to a stepped waveguide of an optical valve at a certain angle may output from points across the first side, with output angle determined by input angle. Advantageously, the stepped waveguide of the optical valve may not require further light redirection films to extract, light towards an observer and angular uoa-auiiormities of input ma not provide non-uniformities across the display surface.

[130] There will BOW be described some waveguides, directional backlights and directional display devices that are based on. and incorporate the structures of FIGURES I to 10 above. Except for the modifications and/or additional features which will now be described, the above descriptio applies equally to the following waveguides, directional backlights and display devices, but for brevity will not be repeated. The waveguides described below ma be incorporated into a directional backlight or a directional display device as described above. Similarly, the directionai backlights described below may be incorporated int a directional display device as described above.

[131] FIGURE HA is a schematic diagram illustrating directional display apparatus comprising a directional displa device and a control system. The arrangement and operation of the control system will now be described and may be applied, with changes as necessary, to each of the display devices disclosed herein. The directional backlight comprises a waveguide 1 and an array 15 of illumination elements I 5a-I5n arranged as described above. The control system is arranged to selectively operate the illumination elements 15a- 15n to direct light into -selectable viewing windows.

[ 132 J The reflective end 4con verges the reflected light. Fresnel lens 62 may be arranged to cooperate with reflective end 4 to achieve viewing windows at a viewing plane. Transmissive spatial light modulator 48 may be arranged to receive the light from, the directional backlight. The image displayed on the SLM 48 may be presented in synchronisation with the illumination of the light sources of the array .15,.

[ 133] The control system may comprise a sensor system arranged to detect the position, of the observer 99 relative to the display device 100. The sensor system comprises a position senso 406_s such as a camera arranged to determine the position of an observer 408; and a head position measurement system 40 that may for example comprise a computer vision image processing system. In FIGURE I IB, the position sensor 406 may comprise known sensors including those comprising cameras and image processing units arranged to detect the position of observer faces. Position sensor 406 may further comprise a stereo sensor arranged to improve the measure of longitudinal, .position compared to a monoseopk camera. Alternatively position sensor 406 may comprise measurement of eye spacing to give a measure of required placement of respective arrays of viewing windows from, tiles of the directional display.

[134] The control system may further comprise an illumination controller and an image controller 403 that, are both supplied with the detected position of the observer supplied from the head position measurement system 404.

[135] The illumination controller comprises an LED controller 402 arranged to determine which light sources of array .15 should be switched to direct light to respecti ve eyes of observer 408 in cooperation with waveguide 1; and an LED driver 400 arranged, to control the operation of light sources of l ight source array 15 by means of drive lines 407. The illumination control ler 74 selects the illuminator elements 15 to be operated in dependence on the position of the observer detected by the head position measurement system 72, so that the viewin windows 26 into which light is directed are in positions corresponding to the left and right eyes of the observer 99. in this manner, the lateral output direciioriality of the waveguide 1. corresponds with the observer position.

[136] The image controller 403 is arranged to control the SLM 48 to display images. To provide an. autostereoscopic display, the image controller 403 and the illumination controller may operate as follows. The image controller 403 controls the SLM 48 to display temporally multiplexed left and right eye images and the LED controller 402 operates the light sources 15 to direct light into viewing windows i positions corresponding to the left and right eyes of an observer synchronously with the display of left and right eye images. In this manner, an autostereoscopic effect is achieved using a time division multiplexing technique, in one example, a single viewin window may be illuminated by operation, of light source 409 (which may comprise one or more LEDs) by means of drive line 41 wherein other drive lines are not driven as described elsewhere.

[137] The head position measurement system 404 detects the position of an observe relative to the display device 100. The LED controller 402 selects the light sources 15 to be operated in dependence on the position of the observer detected by the head position -measurement system 404, so that the viewing windows into which light is directed are in. positions corresponding to the left and right eyes of the observer . In this manner, the output directionality of the waveguide i may be achieved to- correspond wit the viewer position so thai a first image may be directed to the observer's right eye in a. first phase and. directed to the observer^' s left eye in a second phase.

[138] FIGURE LIB is schematic diagram illustrating a left side region of insufficient illumination for right sided off-axis viewing of a directional backlight. The region of insufficient Illumination may be referred to herein as a void region or outer portion 1.20. FIGURE 12A is a schematic diagram illustrating a right side region of insufficient illumination for left sided off- axis viewing of a directional backlight. Further, FIGURES 1 1 B and 12A illustrate the divergence, reflection refraction and extraction of rays emanating from right and left positioned off-axis sources that propagate away from the guide to form corresponding off-axis viewing windows 26 for the optical valve. Thus a directional backlight comprises a waveguide 1 arranged as described above.

[139] A light source 243 of the array 15 may be arranged on the optical axis 238 of a waveguide 1 that is arranged with a substantially rectangular output area (ignoring the sag of the side 4). Diverging light rays from the source 243 are converged by the reflective side 4 to produce a collimated beam within the waveguide with light rays 245, 247 that are parallel to the sides 244, 246 of the waveguide 1. Thus for light source 243, light may be output from across the entire width of the waveguide L

[140] Side 4 comprises a reflective end. that converges the reflected light such, that light sources that are offset from the optical axis of the waveguide fail to illuminate outer portions of the waveguide. The convergence of reflective end defines convergence applied to the incoming light beam from the respective light source. The convergence does not refer to the convergence of the light beam. Thus the light beam that is reflected from the reflective end may be -collimated or converging, but may also be diverging with a divergence that is lower than the divergence of the incident lisht beam on the reflective end. Thus the reflective end converses the reflected light such, that reflected, light from light sources that are offset from the optica! axis of the waveguide fails to illuminate outer portions 120 of the waveguide L

[141 ] The effect of the redirection of these rays off the imaging mirror/lens in the two systems is t create void regions in outer portions 120 within the extraction region thai is substantially void of light. When viewed from the left side of the illuminator, the - triangular voided regio .may appear to the right, and the triangular voided region .may increase in size the further off-axis the viewer moves. A similar triangular portion 120 may be seen symmetrically on the left to viewers situated to the right. To the viewer these portions 120 appear dim. In some cases it may be practical to oversize the extraction region (comprising features 10,12) to avoid an overlap of these deficient portions with the active area of the display panel. It is more desirable to avoid light deficiency and any associated brightness non-uniformity over the entire extraction region for all viewing angles without oversizing and/or to achieve high angle performance compatible with conventional 2D illumination.

[142] FIGURE 12B is a. schematic diagram illustrating the top view of a directional backlight arranged to reduce the visibility of the void outer portions 120, Reflective end at side 4 for a cotliraated output may be provided by form 25 L However, if the radius of curvature is increased to provide reflective end with form 253. Such a form for side 4 produces diverging light beam within the waveguide .1 after reflection., such that the light ray 255 next to side 246 is parallel or close to parallel to side 246, Thus the size of the portion 120 is reduced or eliminated. Further the side 4 may be planar. Such an arrangement thus advantageously reduces the siate of waveguide needed for a gi ven display area and viewing angle. Disadvantageous!}¹, the optimum viewing window distance varies down the length of the waveguide 1 , Such a variation in viewing window performance changes the imaging properties of the waveguide in the vertical direction so that cross talk, image flicker for a moving observer and brightness may vary in. the vertical direction.

[143] The following apparatuses are based on and- incorporate the structures of FIGURES 1 to .10. Accordingly, except for the modifications and/or additional .features which will now be described, the above description applies to the following apparatuses but for brevity will not be repeated.

[ 144] FIGURE 12C is a schematic diagram illustrating a directional display device comprising a directional backlight as described above and spatial light modulator 48 that extends across only part, of the area of the waveguide 1, Thus the entirety of the SLM 48 is outside the outer portions 120, 223 not illuminated by the edge light source 14, Advantageously SLM 48 with border 22.1 does not receive light .from the portion 120 when, directed to viewing window 26 so that a viewer does not have visibility of portions 120. 223. [145] FIGURE I I> is a schematic diagram illustrating a directional display device comprising a directional backlight as described above and a spatial light modulator 48 that, extends across only pari of the area of the waveguide 1. Thus the entirety of the SLM 48 is outside the outer portions not ilm inated by the edge light sources 14. in this example, the sides 225, 227 of the waveguide 1 extending between the input end 2 and the reflective end 4 are diverge from the input end2 to the reflective end , such that the waveguide 1 is tapered. Thus the width of the end 4 is gr ater than th width, of the end 2, The SLM 4$ has a border 22 ! that is inside the. waveguide area to avoid the vi sibility of tie non-waveguide regions. Advantageously the size of the waveguide I is reduced so that additional components 229 such as electronic components may be introduced in the region that would otherwise be void.

[146] The embodiments of FIGURES I2C and 12D increase the size of the directional display device and so it would he desirable to fill the portions in other ways, as will be described in the following embodiments.

[147] FIGURE 13 A is a schematic diagram illustrating an. imaging directional backlight includin a waveguide 1 as described above, wherein the sides 234, 236 of the waveguide 1 extending between the input end 2 and the reflective end 4 and between the guiding -surface^'s,, that are planar surfaces arranged to reflect light into voided portions 120 formed by source 14. Further, FIGURE 13 A is an embodiment in which the sides 234 a d 236 of the waveguide 1 may be polished and optionally coated with a broadband anti-reflection (BBAR) coating. The sides 234 and. 236 may have a reflective coating or may reflect by total internal reflection in which case they need not have a reflective coating. Portion 120, .may be substantially devoid of returning illuminating rays originally from source 14 with position 249 (that may be referred to as the first light source) and reflected at end 4._; In. this example, the sides 234 and 236 are parallel to each other and the optical ax is of the wavegni.de.

[148] When light source 14 (referred to as the as a first light source is operated, light source 232 (referred to as the second light source) positioned on the opposite side of the optical axis 238 and with position 261 approximately equidistant a position 249 may be simultaneously operated to direct light into- the same viewing window as die first light source 14._; Light ray 1 2 undergoes reflection at the side 234 closest to the portion 120. The reflection may be achieved b a metallic coating on side 234 or preferably by total internal reflection. Thus light ra 233 may be parallel, to light ra 235 in the 'waveguide 1. Thus ligh rays with the desired directionality may he arranged to propagate within the void region formed by the first source 1 . m this maimer, Sight rays from first light source 14 and second light source 232 are directed into the same viewing window and the waveguide area that directs light to the viewing window for a given off axis position is increased. Furthe the side 4 may be arranged to achieve eollirnated light within the waveguide, so thai the imaging performance of the waveguide is substantially the same for all. vertical positions. Advantageously for a given SLM. 48 size, the width of tire wa veguide may be reduced, thus reducing bezel size and cost

[149] Thus source 14 and 232 may be arranged to be illuminated in synchronisation with the timing of presentation of one image on an SLM. Thus sources 14 and 232 may be left eye illumination sources for example. Further, the sources of the array 15 may each comprise multiple Sight emitting elements and the gaps ^'between the sources may be substantially reduced or removed.

[ 150] Such a display may be arranged to achieve aotostereosco ic ^'illumination over a wide viewing angle with illumination over the most or all of the waveguide area,

[151] Further, by turning on all sources of the illuminator arra 15, substantially few to no voided portions 120 may then exist and wide angle 2D illumination may be achieved.

[1523 FIGURE 138 is a schematic diagram illustrating a folded imaging directional backlight including a waveguide 1 having polished transmitting edges to direct light substantiall into voided regions between pairs of sources 14, 232. while allowing unwanted rays to exit the guide. Further FIGURE 13B shows that light rays 239 reflected from the side 234 -from sotirce 14 may exit the system through side 236, thus substantially a voiding any stray light contamination of the system and advantageously reducing image cross talk, and display uniformity.

[ 153] FIGURE 14 A is a schematic diagram illustrating operation of a folded imaging directional backlight, with paired sources for increased illumination areas. Further, FIGURE HA illustrates the symmetrical in-filling of voided regions 247 and 248 by source pairs 242 and 243. This paired operation, may substantially prevent any voided regions and can be used for directional .illumination applications such, as an autostereoscopic display. For example in FIGURE 14B sources 2444 may be used to illuminate a left eye image and sources 245, a right eye image, FIGURE Ί.4Β is a schematic diagram illustrating operation, of a directional backlight ^•with, paired sources for increased ilhmrination area on the waveguide 1. Furthermore, this arrangement may be achieved for most to all situations in which the source pairs 242, 243 do not substantially overlap.

[154] FIGURE 14C is a schematic diagram illustrating operation of a directional backlight for on-axis viewing. In the central viewing position the respective left and right eye light sources 263, 265 are typically arranged either side of the optica! axis 238. it would he desirable to illuminate source 263 to illuminate portion 267 arid illuminate source 265 to illuminate portion 269. .However, such sources are in the opposite phase when acting as the first source to the second source, so would, create cross talk in a 3D mode. Thus such an arrangement advantageously achieves 2D infilling of outer portions 267, 269 but some void regions remain in 3D operation. Therefore it .may be desirable to slightly oversize the waveguide 1 in comparison to the SUM 48 to avoi d visibility of the porti ons 267, 269 so that the spatial light modulator 48 extends across only part of the area of the waveguide 1 as described above.

[155] Thus there may be substantially total overlap which may cause single sources 2464, 247 to be used and void regions 246 to exist. Paired operation at high angle, can however, increase stereo viewing angle without introducing void regions larger than those see for near normal viewing.

[156] The apparatus m be operated, by the control system shown in FIGURE 1 .1 A as described above. ^'FIGURE 15 is a schematic diagram illustrating the operation of the control system to further provide driving of the second light source 232 in cooperation with the first light source 14.

[ 157] FIGURE 1.5 is a schematic diagram illustrating a directional display apparatus including a control system 406, 404, 402, 400, and directional, display device including a light source array 15 and a directional waveguide 1 comprising reflective sides 234, 236 arranged to achieve tilling of void outer portions 120 formed by a first light source 14 by illuminating a second light source 232. Thus drive line 41 1 is driven to illuminate light source 14 that creates void outer portion 120, Portion 120 may receive illumination from light, source 232 driven by line 412, light ray 233 from source 234 is directed towards the converging mirro at side 4 and reflected towards side 234 at which surface it undergoes a reflection and is directed parallel to ray 235. Thus light rays with the same output, directionality (and thus directed to the same viewing window) can be achieved in. the portion 1.20 created by source 14. Advantageously, the waveguide I can. be seen to produce light across its entire area tor an. observer in the respective viewing window 26. The size of the illuminated area is thus increased and waveguide 1 size for a given SLM 48 size may be reduced which reduces bezel size and device cost. Further illumination uniformity is increased and viewing freedom may be extended.

[158] Thus a directional backlight comprises a waveguide 1 extending between an input end 2 for receiving input light and a. reflective side 4 for reflecting the input light back through the waveguide, the waveguide 3 having first and second, opposed guide surfaces (comprising side 6 and features .10, 1.2 respectively) extending between the Input end 2 and the reflective side 4 for guiding light forwards and back along the waveguide 1 , wherein the second guide surface has a pluralit of light extraction features 12 facing the reflective end 4 and arranged to reflect the iight guided back through, the waveguide 1 from the reflective side 4 from different input positions across the input end 2 i different directions through the first guide surface 6 thai are dependent on the input position; an array of light sources 15 at different Input positions across th input end 2 of the waveguide I ; and a control system arranged to selectively operate the light sources 14, 232 to direct light into selectable viewing windows 26, wherein the reflective end 4 converges the reflected light such that reflected light from light sources 14 that are offset from the optical axis of the waveguide fails to illuminate outer portions 120 of the waveguide 1 , the waveguide further comprises sides 234, 236, extending between the input end 2 and the reflective end 4 and between the guiding surfaces, that are planar surfaces arranged to reflect light from the iight sources 232, and the control system 406, 404, 402, 400 being arranged, on selective operation of a first light source 14 to direct light into a viewing window 26, to simultaneously operate a second light source 232 that directs light reflected by the reflective end 4 and then by a side 234 of the waveguide .1 into the outer portion .120 of the waveguide I that fails to be illuminated by the first light source 14.

[1 59] The second tight source 232 may selected to direct light into the same viewing window 26 as the first light source .14. The sides 234, 236 of the waveguide I may be parallel. The sides 234, 236 of the waveguide 1 .may be arranged to reflect light from the light sources by total internal reflection. The sides 234, 236 of the waveguide 1 may have a reflective coating. [160] Further a display apparatus may comprise a directional backlight apparatus and a transmissive spatial light modulator 48 extending across the directional backlight apparatus for modulating the light output therefrom. The spatial light modulator 48 ma extends across the first guide surface 6 of the waveguide 1 , The display apparatus may be an auto-stereoscopic display apparatus, wherein the control system is arranged to control the spatial light modulator 48 to display temporally multiplexed left and right eye images and synchronously to operate the light sources to direct light into viewing windows 26 in positions corresponding to the left and right eyes of an observer 408. The display may further comprise a sensor system arranged to detect the position of an observer 408 relative to the display device, the control system to direct the displayed images into viewing windows 26 in positions corresponding to the left and right eyes of the observer 408, i n dependence on the detected position of the observer.

[161] Embodiments wherein the sides 244, 246 of the waveguide 1 are non-parallel can advantageously achieve desirable differences in. the relative positions 249, 261 of the first light source 14 and second light source 232

[162) FIGURE 16A is a schematic diagram illustrating top view of a directional display device comprising a stepped waveguide 1 wherein the sides 244, 246 of the waveguide diverge with an angle 255 from the input end 2 to the reflective end 4, Thus position 261 is a smaller distance from the optical axis 238 than position 249. Light rays 162 from second source 23 are thus directed after reflection at side 244 to be within the portion. 120 such that reflected ray 233 is parallel to the reflected ray 235 from the first source 14 and is directed to the same viewing window. Advantageously; the waveguide has a taper region so that electronics or other components 229 can be positioned in the taper region, reducing usage fey the waveguide 1 of areas outside the display bezel . By control of position, of source 232 with respect to axis 238. the void portions 120 can be filled. Further, as the source 232 is closer to the optical axis 238, the brightness output of the illumination from second source 232 can be more closely matched to the brightness of the illumination, from first source 14 as will be described below,

[163] FIGURE 16B is a schematic diagram illustrating a top view of a directional display device comprising a stepped, waveguide I wherein the sides 244, 246 of the waveguide diverge with a angle 255 from the input end 2 to the reflective end 4. For on-axis viewing positions, it .may not be possible to provide compensating sources such as source 2.32 FIGURE 16A ^•without generating image cross talk. For example the compensating source for a ..right eye viewing window may be the same source to achieve the respective left eye viewing window. Thus, the compensation, will create undesirable image cross talk. Such sources may be termed non-compensaiable sources. Light rays 504 from the edge of non-compensatable source 500 are thus directed by side 4 to form, void region 502. Such void region cannot be filled by a compensating light sources without said source creating image cross talk, such as would be the case if source 501 were .illuminated. Thus the stepped, waveguide 1 most have a minimum width that is oversized by a distance 506 at each side in comparison, to the width of the spatial light modulator 48.

[ 164] Huts if the reflector at the end 4 is arranged to provide collimated light from a single light source of the array 15, then the width of the input side 2 may be oversized by distance 506 so that light sources that are off-axis by a small distance are arranged to fill, die aperture of the spatial light modulator 48. The small distance may for example be the distance from the axis 238 thai provides viewing window in the window plane 106 that are offset by 65mm to ^'90mm. Advantageously left, eye void regions may avoid illumination by compensating light sources that are in the right phase arid vice versa,

[165] .Advantageously., oversizmg the stepped waveguide 1 can achieve a uniform illumination for viewing positions close to the optical axis of the display.,

[ 166] FIGURE- 16 is a schematic diagram illustrating a top view of a directional display device comprising a non-collimating reflecting end 4. in a similar manner to that described for FIGURE 12B, the form. 25.1 (comprising at least a radius and conic constant) of the end 4 that provides collimated output from source 500 after reflection is replaced by a form 25.3 (comprising a radius that is larger than the radius of form 25.1.) that provides diverging output from source 500 after reflection of light rays 504. Further angle 255 for the sides 246 is provided to ch eve rilling of voids for light, sources that are more off-axis than source 500. In comparison to FIGURE Ι.2Β_» the light source array is not required to fill the entire width of the input side 2 to achieve wide angle viewing characteristics. Advantageously void region 502 of FiGURE 1 B are eliminated and the oversize distatice 506 is reduced or removed. Further, light source array 15 has a reduced cost in comparison to the parallel sided arrangement of FIGURE 12B. 167] FIGURE 161> is a schematic diagram illustrating a top view of a directional display device comprising a tapered waveguide 1. wherein the sides 244, 246 of the waveguide converge with an angle 257 from the input end 2 to the reflective end 4.

[168] Thus position 261 is a larger distance from the optical axis 238 than position 249. Light rays 1 2 from second source 232- are thus directed after reflection at side 244 to be within the portion 120 such that reflected ray 233 is parallel to the reflected ray 235 from the -first source 1 and is directed to the same viewing window. Advantageously, the waveguide 1 has a taper region so that electronics or other components 229 can be positioned in the taper region, reducing usage by the waveguide I of areas oatside th display bezel. By control of position of source 232 with respect to axis 238, the void portions J 20 ca b filled. Further, as the source 232 is further from the optical axis 238, the size of the zones 267, 269 as shown in FIGURE 14C ^•for viewing positions that are close to the optical axis are reduced, as the second light source 232 can be switched on at smaller off-axis viewing positions without creating undesirable- image cross talk. Advantageously the bezel size and waveguide cost can be reduced,

[ 169] FIGURE 16E is a schematic illustration of the front view of directional display apparatus comprising outer strings of light sources. LED drtver 400 is arranged to independently drive arra 15 of light sources as described above. It would be desirable to reduce the cost of LED driving for regions at the edge of th viewing freedom, for example in the 2D regions. Further light sources 452 thai ma be driven by drive lines 454 and may be arranged as LED strings for example may be- arranged, at the edges of the array 15, with multiple LEDs driven by a single driver 450. Fewer light sources 452 may be used per unit length of input aperture compared to light sources of array 15. Advantageously, wide angle operation may be achieved, for example in cooperation with, diffuse* 256, and light source cost and driver cost may be reduced in comparison to light sources of array 1-5 that are independently driven.

[170] FIGURE 17 A shows an embodiment of a tracked directional display apparatus in which a camera 5202 and observer position sensing system (not shown) cooperate with light emitting element illuminator array 15 to produce a sub-window array 5204. An observer may be positioned so that right eye 5206 position is arranged near the end of the sub-wi dow array 5204. The illumination from light emitting element illuminator array 15 may demonstrate two artefacts when seen on the surface of optical valve 5200: dark triangle portio 5210 (primarily due to imaging of the side 4 of the optical val ve when directing light to an off-axis position); and a dark band artefact 5208 (primarily due to imaging of ihe light emitting element arrays when observed from a longitudinal position away from the window plane). The dark band artefact 5208 may not be visible at the window plane and the portion 5210 may be seen at and away from the window plane. Advantageously the visibility of these artefacts -which primarily depend on the observer's position, may be detected by one or both of the camera 5202 and observer position sensing tracking/system.. After detection,, appropriate action may be taken as described herein to minimize the visibility of die artefacts 5208, 5210.

[17.1 ] FIGURE 178 Illustrate schematically an embodiment of a tracked directional display apparatus when the observer's eye position 5206 is at the other side of the window array 5204 and the portion 5210 and black bar artefact 5208 are reversed with respect to FIGURE 7A.

[172 ] FIGURE 17C illustrates schematically an embodiment of a directional display apparatus in which the appearance of the black portion 5210 may be compensated by turning on additional sub-windows 5214 b addressing respective light emitting elements 14, 232 of the illuminator array 15, . For an observer with, right eye 5206 position at the right hand side of sub-window array 5204, the respective sub-windows 5214 are- reflected by the edge 5216 and appear substantially overlayed at position 5218. Such: subwtndows 5214 thus illuminate the portion 5210. Advantageously the appearance of the dark triangles 5210 may be compensated or "filled in" by sub- window illuminators 5214, which may be primarily or only seen by the observer reflected at position 52 8. Advantageously the optical losses that result from the different path travelled following reflection at S216, when compared with direct travel for the rest of sub- window array 5204, may be primarily compensated, for by adjusting the intensity of sub windows 521 or 5204. Further, aberration differences such as due to coma .may be compensated for b adjustment of the respective subwindo w 5214 posi tions,

[00277] FIGURE 17P illustrates schematically further embodiment of a directional displa apparatus in which the portion 5210 may be compensated by adjusting the illumination of the SIM 5220 in the respective triangle region. For a known observer eye 5206 position, the ^•position, and the shape of the portion 5210 can be determined, and thus the image may ^'he- updated in correspondence. The difference in. intensity in the triangle 5210 compared to the rest of illumination. 5200 may be compensated by adjusting the transmission of the SIM 5220. Specifically, the image data for the SLM 5220 in region 5222 may be slightly attenuated compared, to region 5224 so that the effect is to match the intensity seen across the whole SLM 5220. The compensation methods described m FIGURES i?C and I7D may be used separately or in combination to improve the viewing regio of the display system. Advantageously, the viewing freedom of the observer can be extended by compensation for the portion 521 .

[173] FIGURE 1 E illustrates a. farther embodiment of a directional display .apparatus- in which the illumination in sub windows 521.4- and illumination at the edge of sub window array 5204 may be adjusted to blend together the transition between, regions 5210 and 5200 and advantageously improve the uniformity of the ilhimi nation seen by the observer in sub-windo 5204. Also illustrated is blending the transmission either side of the boundary between regions 5222 and 5224 of SLM 5220. Such blending may include intensity and or colour blending. Advantageously these two methods may be used singly or in combination to improve the uniformity of the display.

[174] FIGURE ISA is a schematic diagram illustrating a directional backlight in which side reflecting facets 172 are introduced to redirect light into voided regions 120 of a directional backlight system. Further, FIGURE 18A shows an embodiment that may employ additional reflecting facets 1.72 with a directional backlight structure. The facets 172 may reflect rays 174 from a source 14 that may otherwise be absorbed by the edge and create regions void of illumination light as described previously. Althoug the angles of the reflected rays 163 do not exactly match the rays 235 reflected from the imaging surface 4, the combined rays from the entire source illuminator array 15 may fill the portion 120 with an appropriate spread in angle for high angle illiunination. The shadowed surfaces 176 can be made absorbing to substantially suppress unwanted reflection from incident rays 178.

[ 175] FIGURE 18B is a schematic diagram illustrating a further directional backlight in which the sides of the waveguide 1 extending between the input end 2 and the reflective end 4 and between the guiding surfaces are arranged to reflect light incident thereon from a light source into the outer portion of the waveguide that fails to be illuminated by that light- source. In particular, the sides each comp ise an. arra of reflecting facets that redirect light into voided portions 120 of a directional backlight system. Further, FIGURE J8B shows a directional backlight related to that of FIGURE .18C in which the bottom facing facet may be substantially transparent which may allow unwanted rays 177 to exit the system. Such rays may be absorbed b an external component (not shown) to reduce stray light in the system.

[176] FIGURE ISC is a schematic diagram illustrating another directional backiight in which side reflecting facets 173 are introduced to redireci light into voided portions 120 of a directional backlight system. Farther, FIGURE .18C shows the geometry for designin the side reflecting facet angles. In some display systems sources 1704 and 1706 may illuminate for 2D purposes, and the sources 1702 ma provide high quality windows fo 3D a d other direction viewing. Then the facet angles ma best be designed to provide the correct reflection from the outermost source of the sources 1702 group. Consider an outer source positioned at approximately y from the center of an optical valve system of approximate width IF and length the approximate facet angle in degrees at the approximate position x along the side .may be given by:

${:^■■. · ss

[177] hi the present embodiments the curved end 4 may further comprise a Fresnel mirror, that is a mirror with substantially the same curvature as a single surface, comprising facets to further reduce its thickness.

[178] Referring to FIGURE ISC wherein the side 246 may comprise faceted portions, in a waveguide I of a. further display backiight, the facet angle may be arranged so angle 255 is the same as 90- . Advantageously the width of the waveguide 1 can be reduced, so that the bezel size may be correspondingly reduced,

[1793 If the array 15 is arranged with an air gap between the light emitting elements and the input side 2 then the illumination angle around the x-axis within the waveguide 1 will be limited to the critical angle, for example Ή-42 degrees within the waveguide. Such an arrangement may not achieve adequate illumination uniformity for off-axis points which require higher angles of illumination. The cone angle of light within the waveguide can be increased by attaching the array 15 to the input side by an inde matching material thus providing a substantially Lanibertian illumination profile around the x~axis within the waveguide.

[ 180] FIGURE 1.9 is a schematic diagram illustrating a further directional backiight in which side holographic films 182 redireci light into voided portions 120 of a directional backlight system. Further, FIGURE 1 is a related embodiment to that of FIGURES 18A-18C in which the reflecting facets 173 may be replaced with a holographic film 182 which has the same optical fraction as reflecting facets. Thus the holographic film 18.2 may correctly reflect rays 184 that may fill the illumination area and may deflect unwanted rays 188 out of the .system.

[1 81] FIGURE 20A is schematic diagram illustrating a directional backlight in which additional light sources 130 are used to introduce light into the side of an imaging directional backlight such as an optical valve comprising a waveguide 1. further, FIGURE 2QA illustrates an embodiment in. which a uniform 2D illuminator can be provided, through a array of additional Haht emitting elements .130 that act as second lieht sources and are disposed a!orsa each side of the waveguid 1 that extends between the input end .2 and the reflective end 4 and arranged to supply light to the outer portions 120 of the waveguide 1. at appropriate angles for off-axis viewing. Light from light source 14 may provide illumination for the extreme right side viewing window in the optical valve system shown. The reflected ray 134 may define the boundary of the associated right side sub-ilinniinaied portion 120. A defining angle for 138 for the extreme void portion 120 in a 16:9 BD illuminated display system may be approximately 42 degrees. To substantially illuminate these regions, LEDs within arrays 130 may inject light into the guide down with a ray cone of approximatel greater than ±21 degrees. An extreme ray 136· injected from source 132 into portion! 20 may match angle 138 to be extracted at the extreme angles of view.

[ 182] The external viewing angles may be magnified from the internal propagation angle 138 through refraction when extracted from the high index guiding material. Typical backlight aspect ratios, for example 16:9, may cause the extreme windows illuminated b corner light sources 14, to be almost 180 degrees off-normal viewing. Filling illumination void portions 120 with, side injected light from. LED arrays 130 in a system with a complete illuminator array 15 may then provide for wide-angle illumination.

[183] FIGURE MB is a schematic diagram illustrating another directional backlight in which additional light sources 130 are used to introduce light into the side of an optical valve, and FIGURE 20C is a schematic diagram illustrating another embodiment in which additional light sources are used to introduce light into the side of an optical valve waveguide 1. Further, FIGURES 20B and 20C are related embodiments in which the side surfaces of the guide may be altered to help couple light into the guide from the external source arrays 130. In FIGURE 20B the sides may be anti-reflection coated with coating 139 whereas in FIGURE 20C the sides of the waveguide 1 may be serrated so that they comprise an array of facets 1300 facing the second light sources 130, thereby offering a more norma! surface to incoming rays. In the example of FIGURE 20C, rays incident on the side surfaces from sources within illuminator array 15 may be allowed to escape the guide and avoid contamination between viewing windows.

[184] FIGURE- 21 is a schematic diagram illustrating a directional backlight in which local arrays of sources launch light at controlled angles for wide angle uniform viewing with independent window control. In particular,, the sides of the waveguide comprise an array of lenses .1302 aligned with respective second light sources 1304 and arranged to control the directio of light supplied from the second light sources 1304. Thus, FIGURE 21 is an embodiment in which the injected light 1308 may be substantially controlled in direction and angular spread from source 1306 by the lenses 1302. Arrays 1304 of independently addressed sources can be turned on and off in a similar fashion to those in the input illuminator array 15 which may allow for precise windows to he formed at extreme- viewing angles from which uniform illumination is observed.

[185] FIGURE 22A is a schematic diagram illustrating a further directional backlight in which a backlight is placed adjacent an optical valve, FIGURE 22B is a schematic diagram illustrating a side view m which a backlight structure 153 is placed behind the waveguide 1. The backlight structure 153 extends across the second snide surface of the directional waveguide 1 and is arranged to provide illumination through the directional waveguide 1 including the outer portions 120 that feil to be illuminated by off et light sources 14.Futther, FIGURES 22 B and 22C illustrate in front and side views respectively, another embodiment in which a backlight structure 153 is placed behind the waveguide 1. In. each of these apparatuses, the transparency of the waveeui.de 1. of imaging directional baekiisht structures advantaaeouslv enables illumination light from additional light sources to be passed through substantially normally with minimal effect. Placing a 2D LCD backlight system 153 directl behind with independent sources 152 may isolate the illumination from each struciitre for independent directional and Lambertian illumination.

[186] FIGURE 2-B illustrates the backlight structure 153 with the components separated, The system components .may include a light source array 152 which may shine light into a wedge- shaped backsight waveguide 154. The light from the source array 152 may eater the backlight guide 154 by an en trance surface located at the thick. eud of the wedge shaped guide 154. Light, may pass down the guide and may he scattered toward an LCD when .rays reflect off structures 155, Light that refracts off the same structures away from the display may be hack reflected from, a Larabertian reflector 156 on. the opposite side of the backlight waveguide 154 from the directional waveguide 1. The crossed prism films 157 and 158 together with a diffusing film 159 are conditioning films that may condition the light for uniform bright ilHuninaiioa. Although the structure of FIGURE 22B may only appear similar in some regards to directional systems,, the structure of FIGURE 228 may not provide independent, control of viewing windows through source imaging.

[187] FIGURE- 22C is a schematic diagram illustrating a further directional backlight in which a backlight is placed behind an optical valve. FIGURE 22C includes a backlight system 153 and source array 152. Additionally, FIGURE 22C illustrates an input illuminator array 1.5 and extraction features 1.500. Further, FIGURE 22C shows an embodiment in which the extraction features 1500 of the optical valve may be coated with a reflector to avoid leakage of light into the lower films while substantially maintaining tr nsparency.

[188] FIGURE 23 is a schematic diagram illustrating a further directional backlight in which the two separate independent source arrays as shown in. FIGURES 22A and 22B, are replaced by a single array 152 as shown in FIGURE 23. The single arra 152 may be physically moved between the entrance of the imaging directional backlight (illustrated in FIGURE 23 is an optical valve structure} and the conventional back light unit 153. In particular, the array 152 of ligh sources is movable between a position shown in the upper drawing in which they illuminate the input end 2 of the directional, waveguide I and a position shown in the lower drawing in which they illuminate the backlight waveguide .154. Thus, the display apparatus is arranged to illuminate the backlight waveguide 154 using with the same array 1.52 of light sources that illuminate the directional backlight 1. The physical movement can be brought about by actuators or by other physical means.

[189] FIGURE^' 24 is a schematic diagram illustrating a directional backlight in which the display apparatus is arranged to illuminate the backlight waveguide 1 4 using with the same array 152 of light sources that illuminate the directional backlight I by the light being switched between illuminating backlight systems. The backlight apparatus comprises an optical structure arranged to direct the light from the array 15 of light sources selectively to the input end of the directional waveguide 1 or to the backlight waveguide 154. In. particular, the light path from a single source array 152 can be altered by means of polarization switching. The emitted light may be polarized by a polarizing element such as a linear polarizing sheet 164 before being modulated in polarization by liquid crystal (LC) switch 166. Light that is vertically polarized may then pass through polarizing beam splitter (PBS) 168 and may enter the optical valve for directional illumination purposes. In another modulating state the switch 166 ma cause the light to be horizontally polarized causing it to be deflected off the PBS 168 and mirror 169 before entering the backlight for 2D illumination. Related embodiments to the embodiment of FIGURE 24 might use other beam deflecting methods and/or devices such as electrically controllable mirrors or those based on electrically deformab!e deflection elements,

[190] FIGURE 25A is a schematic diagram illustrating a directional display device including a waveguide structure wherein an angle dependent diffuses: film 256 extending across the waveguide 1 is used to diffuse high angle rays to a greater extent than those directed normally from the imaging directional backlight. Further, FIGURE 25 A. shows a waveguide with voided portions 120 which have been substantially filled b any one of the embodiments previously discussed, with an additional angle dependent difftiser film 256, Diffuse* film 256 may have a property that it does not angularly diffuse light incident at angles in a first range around the normal to the film in the lateral direction, but does angularly diffuse incident light at higher angles, that is at angles in a second range in the lateral direction outside the first range. Thus, the dif&ser film appears clear or non-scattering to near-normally incident light. Thus viewing window 26 is achieved for on-axis imaging while viewing window 258 of greater lateral extent is achieved for off-axis imaging. Advantageously the viewing angle of the display for 213 viewing can be increased.

[1 1 ] FIGURE 25B is a schematic diagram illustrating the operation of and a side view of an angular dependent difftiser film 256 perpendicular to the lateral direction. In a system similar to the embodiment of FIGURE 25A, this component may act to mix high angle rays providing 2D viewing capability while substantially maintaining the accurate imaging of near normal light for purposes such as 3D autostereoscopic viewing. [ 1 21 FIGURE 25C is a schematic diagram illustrating one example embodiment, of a high angle diffuser. Film 256 comprises a support layer 2510 has a layer 2512 formed thereon comprising a monomeric mixture with, inclined regions 2514 of Sow refractive index alternating, with regions 2516 of high refractive index therebetween. The regions 2514 and 2516 are inclined with, respect to the normal of the .film 256,. Although this example Includes two regions of 2 14 and 2516 of differing refractive index, i general there may be additional regions of differing refractive index. Light rays 2508 that are incident close to the inclination angle of the regions 2514, 2516 may be scattered that, may be due to total internal reflection between layers 2514, 2516 while light rays 2504 that are incident awa from the inclination angle of the regions 2514, 2516 may be directly transmitted. Multiple scatterin directions can be achieved by stacking films arranged at an angle to each other so that a central clear window may be achieved with outer diffusing regions in horizontal directions or horizontal and vertical directions. At very high incident angles, the film may no longer scatter the light Thus the film 256 may be substantially transparent in a first range, which in this example is from 0 degrees to 25 degr ees, with respect to the normal to the film 256 and may be substantially scattering in a second range, which in this example is from 25 degrees to 55 degrees, with respect to the normal to the film 256.

[1 3] An example of a high angle diffuser film is provided by Sumitomo Chemical Co., LTD. under the tradeniarked product name 'l-umisty",

[ 194] FIGURE 25D is a schematic diagram illustrating an arrangement of an angular dependent diffuser in an aiitostereoscopic directional display device arranged to provide wide angle viewing.. Diffuser 256 is arranged extending across the display apparatus between Fresnel lens 62 and asymmetric diffuser 68, Diffuser 256 may comprise: a first layer 2561 arranged to angularly diffuse light in a sub-range from -t-25 and ÷55 degrees in the horizontal direction with respect to the normal to the diffuser 256 and. substantially not angularly diffuse light outside this input ray angle cone; and a second layer 2561 arranged to angularl diffuse light in a sub-range from -25 and -55 degrees in the horizontal direction with respect to the normal to the diffuser 256. As a result the diffuser 256 diffuses light in a second range from 25 to 55 degrees with respect to the normal and substantially does not diffuse light outside this viewing cone and in a first range within 25 degrees with respect to the normal. Further layers can be added to provide diffusio in the vertical direction if re uired. [195] As described above, the co trol system is arranged hi 3D mode of operation to selectively operate the light sources to direct light into the viewing windows in positions corresponding to the left and right eyes of the observer, for example, using a time division multiplexing technique. The control system is also arranged to operate in a ID mode of operation, for example by continuously displaying the same image across the SLM 48, Advantageously the film may provide increased viewing angle for 2D mode of operation in a thin layer at low cost. In operation, for a tracked observer 408 close to the ott-axis position the display operates as an autosiereoscopic display and film 256 has substantially no effect on output characteristics of the display.. When the observer gets to higher angle positions, the observer tracking system may determine that autosiereoscopic operation is no longer required and switch to 2D operation. In this case, all the light sources of the array 15 may be illuminated. In the illumination directions that are greater than 25 degrees, the diffuser may provide increased viewing angle for sparsely separated light sources. This may reduce the number and intensity and colour matching specification of indi vidually controllable light sources of array 15 and edge iight sources 1.304 (if present) advantageously reducing cost of light sources and control system. Advantageously the layers 62, 256, 68 may be arranged into a single structure to reduce light loss and complexity.

196] Thus an tostereoscopie display apparatus a comprise a display device including an SLM 48 comprising an. array of pixels, the display device being controllable to direct an image displayed o all of the pixels into selectable viewing windows 26 having different positions; and a control system that is operable in a 3D mode of operation and a 2D mode of operation, the control system being arranged in the 3D mode of operation to control the display device to display temporally multiplexed left and right images and synchronously to direct the displayed images into viewing windows .26 in positions corresponding to the left and right eyes of the observer 408, and being arranged i the 2D mode of operation to control the display device to display a continuous 2D image, wherein the display device 48 further comprises an- angle- dependent diffuser film 256 extending across the display device 48 having a propert that light incident at angles i a first range around the normal to ire film 256 is not angularl diffused but light incident at angles in a second range outside said first range is angularly diffused. [ 197] The embodiment of FIGURE 25D can be combined with any of the other wide angle embodiments described herein,. In general, such, a diffuser film, may achieve similar advantages when applied extending across any type of autostereoseopic display apparatus that is operable in a 3D mode of operation using a time division multiplexing technique and also a 2D mode of operation.

[198] FIGURE 26 is a schematic diagram illustrating a directional backlight in which illuminating light is diffused, using a swiiohab!e diffusing element. Further, FIGURE 26 shows schematically an embodiment that ma redirect imaging rays using a switchable diffoser. Light rays J 94 may be emitted from, the imaging directional backlight structure and may form source images within a window plane for directional illumination. A switchable diffoser such as a polymer dispersed liquid crystal device 192 may have minimal effect on the rays in a first state. Electrically altering the first state into a different state that is diffusing may act to break the imaging condition and spread the light 196 substantially uniformly for wide angle 2D viewing.

[1 9] FIGURE 27 is a schematic diagram illustrating a directional backlight in which guided light may be extracted in a diffuse form by optically contacting the bottom surface, of a directional backlight with a diffuse reflecting element 202 comprising a structured side with features 203, 205 and a diffusing side comprising a diffusing surface 209. Further, FIGURE 27 is a further embodiment in which the imaging condition, of an imaging directional backlight may be broken through the introduction of a diffuser. In FIGURE 27, a reflecting diffusing element 202 may be made to be opticall isolated in one state and in optical contact with the light extraction features in another state. In the first state light may not interact with the diffusing element 202. Making optical contact through physically moving the element 202 toward the guide may allow light to penetrate the diffuser structure by breaking the total internal reflection condition at the light extraction regions 12.. I the second state air gaps 207 ma be provided by inclined sides 203, 205, J O. 32 to achieve guiding for light passing in the first direction through the waveguide 1. The resulting diffuse light 206 may provide desired wide angle 2D illumination.

[200] FIGURE 28 is a schematic diagram illustrating a directional backlight in which guided light may be extracted in a dif&se form b optically contacting the bottom surface of an imaging directional backlight with a dif&se reflecting element through electrofonning material surface .material, and FIGURE 29 is a schemati diagram illustrating of yet another embodiment in which electro-wetting material is -made to move from behind reflecting facets into the guiding .region of an optical valve forcing light to exit and reflect off a diffusing surface. Alternative methods of makine. optical contact between a lower reflecting diffuse* element and an imagine directional backlight can be considered such as electrofonning polymers 2 14 or electro-wetting materials 2.1.8 as illustrated in FIGURES 28 and 29 respectively.

[203 ] It is understood thai in the above embodiments that a full directional backlight may include additional. Fresnel and diffusing elements.

[202] IGURE 30 is a schematic diagram illustrating a front view of an autostereoscopic display device comprising wedge directional backlight and comprising angled sides 1244. 1246. FIGURE 31 is a schematic diagram illustrating a side view of an autostereoscopic display device comprising a wedge directional backlight arranged to achieve landscape and portrait operation. Wedge directional backlights are described in United States Patent ^'No. 7,660,04? incorporated herein by reference. The optical wedge 13.04 is a waveguide having an input end and first and second, opposed guide surfaces 1 106 for guiding light along the optical wedge 1 104 that are both planar. The optical wedge ! 104 is illuminated by light source array 1 01 and light propagates within the medium 1104 of the wedge by total internal reflection at the guide surfaces 1 106. The optical wedge ! 1.04 has a. reflective end 1 102 formed by a corrugated mirror facing the input end for reflecting light from the input end back through the optical wedge 1 1.04. The second suide surface is inclined at an anale to reflect liaht in directions that break the total internal reflection of the first guide surface after reflection at the reflective end 1 102, so that light is output at the first guide surface by refraction of light.

[203] By way of comparison with the stepped imaging directional backlight, light extraction features are not provided. However, the operation is similar m thai the optical wedge 1 104 directs input light from the light sources of the light source array 1.101 at different input positions across the input end. in output directions relative to the normal to the first guide surface that are dependent on those input positions, A control system as described above with reference to FiGU Es 1 1 A and 1 IB is arranged to selectively operate the light sources to direct light into the viewing windows in positions corresponding to the left and right eyes of the observer.

[204] The optical wedge 1 104 extends across a transraissive spatial light modulator 1 1 10 to which the output light is supplied. The spatial light modulator 1.1. 1.0 comprises an array of pixels that modulate light arranged in an aperture with a shape having two perpendic ular axes of mirror symmetry. Since light is output from the optical wedge 1 104 at high, angles of refraction, a prismatic element 1 08 extendim across first auide surface of the optical wecke 1 104 acts as a deflection element to deflect light ¾ywards the normal to the spatial light modulator J 10.

[205] Sloped sides 1244, 1246 may be arranged in a similar manner to that shown in FIGURE 28 to achieve filling of void portion 120.

[206] The embodiments related to stepped waveguide directional backlights may b applied with changes as necessary to the wedge directional backlight as described herein.

[207] As may be used herein, the terms "substantially" and ''approximately" provide an industry-accepted tolerance for its corresponding term and/or relativity between items. Such an industry-accepted tolerance ranges from zero percent to ten percent and corresponds to, but is not limited to, component values, angles, et cetera. Such relativity between items ranges between approximately zero percent to ten percent.

[208] While various embodiments in accordance with the principles disclosed herein have been described above, it should be understood that the have been presented by way of example only, and not limitation. Thus, the breadth and. scope of this disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in. accordance with any claims and their equivalents issuing from this disclosure. Furthermore, the above advantages and features are provided in described embodi ments, but shall not limit the application of such issued claims to processes and. structures accomplishing any or all of the above advantages.

[209] Additionally, the section headings herein are provided for consistenc with the suggestions under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the embodiments) set out in. any claims tha may issue from this disclosure. Specifically and by way of example, although the headings refer t a "'Technical Field," the claims should not be limited by the language chosen under this heading to describe the so-called field. Further, a description of a technology in the "Background" is not to be construed as aft admissio that certain technology Is prior art to any embodiments) in this disclosure. Neithe is the "Snmraaty" to be considered as a characterization of the embodiments) set forth in issued claims. Furthermore, any reference in this disclosure to "invention" in. the singular should not be used to argue that there is only a single point of no velty in this, disclosure. Multiple embodiments may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the embodiments), and their equivalents, that are protected thereby, in all instances, the scope of such ciaims shall be considered on their own merits in light of this disclosure, but should not be constrained b the headings set forth herein_*

Claims

.! . A directional backlight apparatus comprising;

a waveguide extending between an input end for receiving input light and a reflective end for reflecting the input light back through the waveguide;

an array of light sources disposed at different input positions in a lateral direction across the input end. of the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding Sight forwards and back along the waveguide, the waveguide being arranged to reflect input, light from light sources at the diff erent input positions across the input end after reflection from the reflecti ve end into respective optical windows in output directions distributed in the lateral direction in dependence on the inpu positions; and

a control system arranged to selectively operate the light sources to direct light into a selectable viewing windows,

wherein

the reflective end converges the reflected light such that reflected light irons light sources that are offset from the optical axis of the waveguide fails to illuminate outer portions of the waveguide,

the waveguide further comprises sides, extending between the input end and the reflective end and between the guiding surfaces, that are planar surfaces arranged to reflect light from the light sources, and

the control system being arranged, on selective operation of a first light source to direct light into a viewing window, to simultaneously operate second, light, source that directs light reflected by the reflecti e end and. then by a side of the waveguide into the outer portion of the waveguide that fails to be illuminated by the first light source,

2. A directional backlight apparatus according to claim 1 , wherein the second light source is selected to direct light into the same viewing window as the first light source.

3. A directional backlight apparatus according to claim 1 or 2, wherein the sides of the waveguide are parallel

4. A directional backlight apparatus according to claim 1 or 2, wherein the sides of the waveguide diverge from, the input end to the reflect e end.

5. A directional backlight apparatus according to claim 1 or 2, wherein the sides of the waveguide converge from the input end to the reflective end.

6. A directional backlight apparatus according to any one of claims I to 5, wherein the sides of the waveguide are arranged to reflect light from the light sources by total internal reflection.

7. A directional backlight apparatus according to any one of claims 1 to 5_S wherein the sides of the waveguide have a reflective coating..

8. A directional backlight apparatus according to any one of claims i to 7, wherein the first guide surface is arranged to guide light by total interna! reflection and the second guide surface comprises a plurality of light extraction features oriented to reflect ligh guided through the waveguide in directions allowing exit through the first guide surface as the output light.

9. A directional backlight apparatus according to claim 8, wherein the light extraction features are facets of the second guide surface,

10. A directional backiiaht apparatus according to claim 9. wherein the second guide surface has a. stepped shape comprising sa d facets and intermediate regions between the facets that are arranged to direct light through the waveguide without extracting it..

1 1. A directional backlight apparatus according to an one of claims I to 7, wherein the first guide surface is arranged to guide light by total internal reflection aad the second guide surface is substantially planar and inclined at an angle to reflect light in directions that break the total internal, reflection for outputting light throug the first guide surface,

the display device further comprising a defection element extending across the first guide surface of the waveguide for deflecting light towards the norma! to the spatial light Modulator. ί 2. A display apparatus comprising;

a directional backlight apparatus according to any one of claims I to 1 1: and

a transmissive spatial light modulator extending across the directional ^'backlight apparatus for modulating the light output therefrom.

13. A display apparatus according to claim 12, wherein the spatial light modulator is disposed across the first guide surface of the waveguide.

14. A display apparatus according to claim. 12 or 13_» being an autostereoscopic display apparatus, wherein the control system is arranged, to control the spatial light modulator to display temporally multiplexed left and right eye images and synchronously to operate the light sources to direct, light into viewing windows in positions corresponding to the left and right eyes of an observer.

15. A display apparatus according to claim 14, further comprising a sensor system arranged to delect the position of an observer relative to the displa device, the control system to direct the displayed images into viewing windows in positions corresponding to the left and right eyes of the observer, in dependence on the detected position of the observer.:.

Hi. A directional backlight comprising:

a waveguide extending between an input end for receiving input light and a reflective end for reflecting the input light back through the waveguide; and

an array of light sources disposed at different input positions in a lateral direction across the input end of the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding l ight forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from, the refieciive end into respective optical windows in output directions distributed in the lateral direction in dependence on the input positions,

wherein

the reflective end converges the reflected; light such that reflected light from light sources that are offset from the optical axis of the waveguide .fails to illuminate outer portions of the waveguide, and

the waveguide further comprises sides, extending between the input end and the reflective end and between the guiding smiaces, that are arranged to reflect the light incident from a light source into the outer portion of the waveguide that fails to be illuminated by that light source,

17. A. directional backlight according to claim 16., wherein the sides each comprise an array of reflective facets.

18. A directional backlight according to claim .16, wherein the sides each comprise a

holographic film..

19. A directional backlight according to any one of claims 16 to 18, wherein the sides are arranged to reflect the light incident from a light source in the same direction as light front that light source that is reflected from the reflective end of the waveguide.

20. A directional backliaht according to any one of claims 16 to 19, wherein the first guide surface is arranged to guid light by total internal reflection and the second guide surface comprises a plurality of ligh extraction features oriented to reflect light guided through the waveguide in directions allowing exit through the first guide surface as the output light.

21. A directional backlight according to claim 20_; wherein the light extraction features are facets of the second guide surface,

22. A directional backlight according to claim 2 ! , wherein the second guide surface has a stepped shape comprising said facets and intermediate regions between the facets that are arranged to direct light through the waveguide without extracting it.

23. A directional backlight according to any one of claims 16 to 19, wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface is substantiall planar and inclined at an angle to reflect Sight in directions that break the total internal reflection for outputting light through the first, guide surface,

the directional, backlight further, comprising a deflectio element extending across the first guide surface of the waveguide for deflecting light towards the norma! to the spatial light modulator.

24. A display device comprising:

a directional backlight according to any one of claims 16 to 23 ; and

a transroissive spatial light modulator extending across the directional backlight apparatus for modulating the light output therefrom.

25. A display device according to claim. 24, wherein the spatial light modulator is disposed across the first guide surface of the waveguide.

26 A display apparatus comprising a display device according to claim 24 or 25, and a control system arranged to selectively operate the light sources to direct, light, into selectable viewing windows.

27. A. display apparatus according to claim 26, being an autostereoscopic display apparatus, wherein, the control system is arranged to control the spatial light modulato to display temporally multiplexed left and right eye images and synchronously to operate the light sources to direct light into viewing windows in positions corresponding to the left and right eyes of an observer.

28. A display apparatus according to claim 27, further comprising a sensor system arranged to detect the position of an observer relative to the display device, the control system to direct the displayed images into viewing windows in positions corresponding to the left and right eyes of the observer. In dependence on the detected position of the observer.:.

29. A directional backlight comprising?

a waveguide extending between an input end for receiving input light and a reflective end for reflecting the input light ack through the waveguide; and

an array of light sources disposed at different input positions m a lateral directio across the input end of the waveguide, the waveguide having first and second, opposed guide .surfaces extending between the input end and the reflective end for guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from the reflective end into -respective optical windows m output directions distributed in the lateral direction in dependence on the input positions,

wherein

the reflective end converges the reflected li ht such that reflected light from light sources that are offset from the optical axis of the waveguide fails to illuminate outer portions of the waveguide, and

the direc tional backlight further comprises an array of second light sources disposed along each side of the waveguide that extends between the input end and the reflective end and between the guiding surfaces and arranged to supply light to said outer portions of the waveguide.

30. A directional backlight according to claim 29, wherein, the sides of the waveguide comprise an array of facets facing the second light sources.

31. A directional backliuht according to claim 30. wherein the sides of the waveguide comprise an array of lenses aligned with respective second light sources and arranged to control the direction of light supplied from, the second light sources.

32. A. directional backlight accordina to anv one of claims 29 to 1.., wherein the first aiti.de surface is arranged to guide light by total internal reflection and the second guide surface comprises a. plurality of light extraction features oriented to reflect light guided through the wa veguide in directions allowing exit through the first guide surface as the output light.

33. A directional backlight according to claim 32, wherein the Sight extraction features are facets of the second guide surface.

34. A directional backlight according to claim 33, wherein the second guide surface has a stepped, shape comprising- said facets and intermediate .regions between, the facets that are arranged to direct light through the waveguide without extracting it,

35. A. directional backlight according to an one of claims 29 to 31, wherein, the ^'first guide surface is arranged to guide light by total internal reflection and the second guide surface is substantially planar and inclined at an angle to reflect light in directions that break the total internal reflection for outputting tight through the .first guide surface,

the display device further comprising, a deflection element extending across the first guide surface of the waveguide for deflecting light to wards the normal to the spatial light- modulato

36. A display device comprising:

a directional backlight according to any one of claims 29 to35 and

a transm.issive spatial light tnoduiator extending across the directional, backlight apparatus for modulating the light output therefrom.

37. A display device according to claim 38, wherein the spatial light modulator is disposed across the first guide surface of the waveguide.

38. A display apparatus comprising a display device according to claim .36 or 37,. and a control system arranged to selectively operate the light sources to direct light into selectable viewing windows.

39. A display apparatus according to claim 38, being an. auiostefeoscppic display apparatus, wherein the control system is arranged to control the spatial light modulator to display temporally multiplexed left and righ eye images and synchronously to operate the light sources to direct light into vi ewing windows in. positions corresponding to the left and right eyes of an observer.

40. A display apparatus according to claim 39, further comprising a sensor system arranged to detect the position, of an observer relative to the display device, the control system to direct the displayed images into viewing windows in positions corresponding to the left and right eyes of the observer , in dependence on the detected position of the observer.

41. A display device comprising:

a waveguide extending between an input end. for receiving input light and reflective end for reflecting the input light back through the waveguide,;

an array of light sources disposed at different input positions in. a lateral direction across the input end of the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end fo guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across the input end after reflection from the reflective end into respective optical windows in. output directions distributed in the lateral, directio in dependence on the input positions; and

a rransmissive spatial light modulator extending across the waveguide for modulating the light output therefrom, wherein the spatial light modulator extends across only pari of the area of the waveguide.

42. A display device according to claim 1, wherein the reflective end converges the reflected light such that reflected light from each light source illuminates all of the part of the waveguide across which the spatial light modulator extends.

43. A disp lay device ac cording to claim 41 or 42, wherein the sides of the waveguide, extending between the input end and the reflective end, diverge from the input end to the reflecti ve end,

44. A display device according to any one of claims 41 to 43, wherein the spatial light modulator is disposed across the first guide surface of the waveguide.

45. A display device according to any one of claims 41 to 44, wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction features oriented to reflect light guided through the waveguide in directions allowing exit through the first guide surface as the output light.

46. A. display device according to claim 45, wherein the light extraction features are facets of the second snide surface.

47. A display device according to claim 46, wherein the second guide surface has a stepped shape comprising said facets and intermediate regions between the facets that are arranged to direct light through, the waveguide without extracting It.

48. A display device according t any one of claims 41 to 44. wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface is substantially planar and inclined at an angle to reflect light i directions that break the total internal reflection for outputting Sight through the first guide surface*

the display device further comprising a deflection element extending across the first guide surface of the waveguide for deflecting light towards the normal, to the spatial light modulator.

49. A display apparatus comprising- a display device according to an one of claim 41 to48, and a control system arranged to selectively operate the light sources to direct light into selectable viewin windows.

50. A display apparatus according to claim 49, being an auiostefeoscqpic display apparatus, wherein the control system is arranged to control the spatial light modulator to display temporally multiplexed left and righ eye images and synchronously to operate the light sources to direct Sight into viewing windows in positions corresponding to the left and right eyes of an observer.

51 , A display apparatus according to claim 50, further comprising a sensor system arranged to detect the positio of an observer relative to the display device, the control system to direct the displayed images into viewing windows in positions corresponding to the left and right eyes of the observer, in dependence on the detected position of the observer.

52, A directional backlight comprising:

a directional waveguide extending between, an input end for receiving input light and a reflective end for reflecting the input light back through the directional^' waveguide, the directional waveguide having first and second, opposed guide surfaces extending between the input end and the reflectiv end for guiding light forwards and hack along the directional waveguide,

wherein the second guide surface has a plurality of light extraction features facing the reflective end and arranged to reflect the light guided back through the directional waveguide front the reflective end from different input positions across the input end in different directions through the first guide surface that are dependent on the input position; and

an array of light sources arranged to illuminate the directional waveguide at different input positions across the input end of the directional waveguide, wherein the reflective end converges the reflected light such that reflected light item light sources that are offset from the optical axis of the directional waveguide rails to illuminate outer portions of the directional waveguide;

a backsight structure arranged extending across the second guid surface of the

directional waveguide and arranged to provide illumination through the directional waveguide including the outer portions that fail to he illuminated by offset light sources,.

53. A directional apparatus according to claim 52, wherein the backlight structure comprises a backlight waveguide.

54. A directional backlight according to claim 53, wherein the backlight waveguide is wedge-shaped.

55. A directional backlight according to claim 53 or 54, wherein the backlight structure further comprises a Lambertian .reflector on. the opposite side of the backlight waveguide from the directional waveguide.

56. A directional backlight according to any one of claims 52 to 55, wherein the backlight structure further comprises at least one conditioning film, arranged between the backlight waveguide and the directional waveguide.

57. A directional backlight according to any one of claims^' 52 to 56, wherein the directional backlight is arranged to iiiuminate the backlight waveguide with said array of light sources that are arranged to illuminate the directional waveguide.

58. A directional backlight according to claim 57, wherein the array of light, sources are movable between a position in which they illuminate the input end of the directional waveguide and a position in which they iiiuminate the backlight waveguide.

55⁾, A directional backlight according to claim 58, further comprising an optical structure arranged to direct the light from the array of light sources selectively to the input end of the directional waveeuide or to the backlight waveaaide.

60, AM autostereoscopk display apparatus, co.mpi-isi.ag:

a display device comprising an array of pixels, the display device being controllable to direct an image displayed on all of the pixels into selectable viewing windows having -different, .positions; and

a control system, that is operable in. a 3 D mode of operation, and a 2D mode of operation, the control sy stem, being arranged in the 3D mode of operation to control the display device to display temporally multiplexed, left and right images and synchronously to direct the displayed images into viewing windows in. positions in a lateral direction correspondin to the left and right eyes of the observer, and being arranged in the 2D mode of operation to control the display device to display a continuous 2D image,

wherein the display device farther comprises an angle-dependent diffuser film extending across the display device having a property that light incident at angles in a first range in the lateral direction around the normal to the film is not angularly diffused but light, incident at angles in a second range in a lateral direction outside said first range is angularly diffused.

61 , An autostereoscopk display apparatus according to claim 60_., wherein the angle dependent, diffuser film comprises a layer comprising regions of material, of differing refractive index that alternate with each other and are inclined with respect to the normal of the film.

62, An autostereoscopk display apparatus according to claim 60 or 61 , wherein the display device comprises :

a waveguide extending between an input end. for receiving input light and a reflective end for reflecting the input light back through the waveguide,;

^•an. array of light sources disposed at different input positions in. a lateral direction across the input end of the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end for guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input light from light sources at the different input positions across die input end after reflection from, the reflective end into respective optical windows in output directions distributed in the lateral direction, in dependence on the input positions; and

a transmissive spatial light modulator comprising said array of pixels arranged to Modulate light that has exited the waveguide; and

the control system being arranged in said 3D mode of operati n to selectively operate the light sources to direct Sight into the viewing windows in positions corresponding to the left and righ eyes of the observer,

63. An aiitostereoscopic display apparatus according to claim 62, wherein the first guide surface is arranged to guide Iight by total interna] reflection and the second guide surface comprises a plurality of light extraction features oriented to reflect light guided through the waveguide in directions allowin exit through the first guide surface as the output light

64. An aiHostereoscopic display apparatus according to claim 63, wherein the light-extraction features are facets of the second guide surface.

65. An autostereoscopie displa apparatus according to claim 64, wherein the second guide surface has a stepped shape comprising said facets and intermediate regions between the facets that are arranged to direct light through the waveguide without extracting it.

66. An aiitostereoscopic display apparatus according to claim 62, wherein the first guide surface is arranged, to guide light by total interna? reflection and the second guide surface i substantially planar and inclined at an angle to reflect light in directions that break the total internal reflection, for outputting light through, the first guide surface,

the autostereoscopie display apparatus further comprising a deflection elemen extending across the first guide surface of the waveguide for deflecting light towards the normal to the spatial light modulator.

67. An autostereoscopie displa apparatus according to any one of claims 62 to66, further comprising a sensor system arranged to detect the position, of an observer, the control system being arranged to direct the displayed images into viewing windows in positions corresponding to the left aod right eyes of the observer in dependence on the detected position of the observer.

68. A waveguide structure comprising:

a waveguide extending between an. Input end for receiving input light and a reflective end for reflecting the input light back through the waveguide, the waveguide having first and second, opposed guide surfaces extending between the input end and the reflective end. f f guiding light forwards and back along the waveguide, the waveguide being arranged to reflect input Sight from different input positions in a lateral direction across the input end after reflection from the reflective end in output directions distributed i the lateral direction in dependence on the input position; and

an angle-dependent diffuser film extending across the waveguide, having a property that light incident at angles in a first range around the normal to the film in the lateral direction is not angularly diffused but light incident at angles in a second range in a. lateral direction outside said range is angularly diffused.

69. A waveguide structure according to claim 68, wherein the angle dependent diffuser film comprises a layer comprising regions of material of differing refractive index that alternate with each other and are inclined with respect to the normal of the film.

70. A waveguide structure according to claim 68 or 69, wherein the angle-dependent diffuser film extends across the entirety of the waveguide.

71. A. wa veguide structure according to any one of claims 68 to 70, wherein, the first guide surface is arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction, features oriented to reflect light guided through the waveguide hi directions allowing exit through the first guide surface as the output light.

72. A waveguide structure according to claim 71, wherein the light extraction features are facets of the second gui de surface.

73. A waveguide structure- according to claim 72, wherein the second, guide surface has a stepped shape comprising said facets and intermediate regions between the facets that are arranged to direct light through the waveguide without extracting it,

74. A waveguide structure according to any one of claims 68 to 70, wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface is substantiall planar and inclined at an angle to reflect Sight in. directions that break the total internal reflection for outputting light through the first, guide surface,

the autostereoscopie display apparatus further co.mp.risi.ag a deflection element extending across the first guide sur ace of the waveguide tor deflecting light towards the normal to the spatial light modulator.

75. A directional backlight comprising a waveguide structure according to any one of claims 68 to74, aad an array of light sources at different input positions across the input end of the waveguide,, the reflective end converging the reflected light such that reflected light from light sources that are offset f om th optical axis of the waveguide fails to illuminate outer portions of the waveauide.

76. A display device comprising;

a directional backlight apparatus according to any one of c laims 68 to 75; and

a rransmissive spatial light modulato extending across the directional backlight, apparatus for modulating the light output therefrom.

77. A display device according to claim 76, wherein the spatial light modulator is disposed across the first guide surface of the waveguide,

78. A display apparatus comprising a display device according to claim 76 or 77, being an autostereoscopic display apparatus further comprising a control system arranged in a 3D mode of operation to control the spatial light modulator to display temporally multiplexed left and right eye images and synchronously to operate the light sources to direct light into viewing windows in positions corresponding to the left and right eyes of an. observer.

79. A display apparatus according to claim 78. further comprising a sensor system arranged to detect the position, of an observer relative to the display device, the control system being arranged in said 3D mode of operation to direct, the displayed images into viewing windows in positions . corresponding to the left and right eyes of the observer, in dependence on the detected position of the observer,

80. A directional illumination apparatus, comprising:

an imaging directional backlight for directing light comprising:

a waveguide for guiding light, further comprising.^'

a first light guiding surface; and

a second light guiding surface, opposite the first, light guiding surface; and an ill animator array for providing light to the imaging directional backlight; and

an additional, optical element that alters the optical system of the imaging directional backlight to provide a substantial ly uniform 2D illumination mode.

81. The directional illumination apparatus of claim 80, wherein the additional optical element further comprises at least an optical emitter.

82. ^'The directional illumination apparatus of claim 80, wherein the additional optical element further comprises at least an imaging facet end,

83. The directional illumination, apparatus of claim 86, wherein, the additional optical element further comprises at least an alternative light path.

84. The directional illumination apparatus of claim 80, wherein the additional optical element, further comprises at least one of a optical emitter, an imaging facet end, or an alternative light path.

85. The directional illumination apparatus of claim 80, wherein the substantially uniform.2D mode is a substantially uniform Lambertian illumination mode.

86. The directional illumination: apparatus of claim 80, wherein the waveguide is an optical valve.

87. The directional illumination apparatus of claim 80, wherein the waveguide is an optical inline directional backlight.

88. The directional ilhimmaiion. apparatus of claim 80, further comprising additional illuminator elements other than the illuminator elements of the i lluminator array,

89. The directional illumination apparatus of claim 88, wherein the additional illuminator elements arranged to provide ^'light to a first side and a second side of the waveguide .

6690 The directional illumination apparatus of claim. 89, wherein the additional illuminator elements may direct light into the waveguide with a ray cone of approximately greater than plus or minus 21 dearees.

91. The directional illumination apparatus of claim 89, wherein the first and second sides of the waveguide are altered, to couple light from the additional illuminator elements into the waveguide,

92. The direction l, illumination apparatus of claim 1., wherein the first and second sides of the waveguide may be anti-reflection coated.

93. The directional illumination apparatus of claim .91 , wherein the first and. second sides of the waveguide may he serrated.

94. The directional illutnmation: apparatus of claim 80, further comprising local arrays of iHiujjinator sources located, at a first side and a second side of the waveguide, wherein the local arrays of illuminator sources provide independent window control

95. The directional illumination apparatus of claim 94, wherein injected light from the local arrays of illuminator soarces may be substantially controlled in direction and angular spread by leasing elements.

96. The directional illumination apparatus of claim 95, wherein the local arrays of illuminator sources are independently addressed sources.

97. A stepped imaging directional backlight apparatus, comprising:

a stepped waveguide for guiding light, wherein the waveguide comprises:

a first light guiding surface; and

a second light guiding surface, opposite the first light guiding surface, the second light guiding surface comprising at least one guiding feature and a plurality of extraction features, wherein the extraction, features direct light to exit the stepped waveguide;

a first illumination input surface located between the first and second light guiding surfaces, the first, illumination input surface operable to receive light from a first array of light sources:

an illuminator array for providing light to the stepped imaging directional backlight; and

an additional optical element that alters the optical system of the stepped imaging directional backlight to provide a substantially uniform 2D illumination mode.

98. The stepped imaging directional backlight apparatus of claim 97, wherein the stepped waveguide further comprises a first section operable to allow light rays to spread.

99. The stepped imaging directional, backlight apparatus of claim 97. wherein the plurality of extraction features directs light to pass with substantially low loss when, the light is propagating in a first direction and directs light to exit the stepped waveguide when the light is propagating in a second direction._*

100, The stepped imaging directional backlight apparatus of claim 97, wherein the stepped waveguide is an optical val ve.,

J 01 , An iniagmg directional backlight, comprising:

an. input side located at a first end of a waveguide;

a reflective side located at a second end of the waveguide;

a first light directing side and a second light directing side located between the input side and the reflective side of the waveguide, wherein the second light directing side further comprises a plurality of guidin features and a plurality of extraction features; and

an additional optical element that alters an optical system of the imaging directional backlight to provide a substantially uniform 2D illumination .mode, wherein the additional optical element is at least one of an optical emitter_* an. imaging facet end, or an alternative light path.

102, The imaging directional backlight of claim 101 _s further comprising a first section operable to allow light r ys to spread and without extraction features,

103. The imaging directional backlight of claim 102, wherein the waveguide is a stepped waveguide.

1.04. The imaging directional backlight of claim .102, -wherein, the imaging directional backlight is an optical valve..

1 5, A folded imaging directional backlight, system that provides a substantially uniform 2D illumination mode, comprising:

a .folded imaging directional backlight, comprising:

a first waveguide for guiding light operable to receive light from an illuminator array; and a second waveguide optically connected to the first waveguide and operable to receive Sight .from the illuminator array, wherein the first waveguide has a first edge with edge facets and the second waveguide has a second edge with edge facets, further wherein th edge facets provide a substantially uniform 2D illumination mode.

106. The folded imaging directional backlight system that provides a substantially uniform 2D illumination mode of claim 105, wherei the edge facets of the - first and second edge are reflecting facets. 07. The folded imaging directional backlight system that, provides a substantially uniform 2D illumination mod of claim 106 , wherein the fi rst and second wa veguides are stepped waveguides,

108. The folded imaging directional backlight system, that provides a substantially uniform.2D illumination mode of claim 105, wherein the folded imaging, directional backlight i an optical valve.

109. The folded imaging directional backlight system, that provides a substantially uniform.2D illumination mode of claim. 106, wherein the first and second waveguides are wedge type directional backlights.